CIHM 
Microfiche 
Series 
(Monographs) 


ICIMH 

Collection  de 
microfiches 
(monographles) 


Canadian  Inatituta  for  Historical  Microraproductions  /  institut  Canadian  da  microraproductions  hittoriquas 


Tachnical  and  Bibliographic  Notas/Notas  tachniquas  at  bibliographiquas 


The  Instituta  haa  attampted  to  obtain  tha  bast 
original  copy  available  for  filming.  Faaturas  of  this 
copy  which  may  ba  bibliographically  unique, 
which  may  altar  any  of  tha  images  in  tha 
reproduction,  or  which  may  significantly  change 
the  usual  method  of  filming,  are  checked  below. 


L'Institut  a  microfilma  la  meilleur  axamplaire 
qu'il  tui  a  at^  possible  de  se  procurer    Las  details 
de  cet  exemplaire  qui  sont  peut-Atre  uniques  du 
point  de  vue  bibliographique,  qui  peuvent  modifier 
una  image  reproduite.  ou  qui  peuvent  exiger  une 
modification  dans  la  mAthoda  normala  de  filmaga 
sont  indiquAs  ci-dessous. 


D 


Coloured  covers/ 
Couverture  da  eouleur 


□    Coloured  pages/ 
Pages  de  eouleur 


D 
D 


Covers  damaged/ 
Couverture  endommagie 

Covers  restored  and/or  laminated/ 
Couverture  restaurAa  et/ou  pelliculAe 


1/ 


n 


Pages  damaged/ 
Pages  endommag^as 

Pages  restored  and/or  laiv' 
Pages  restaurees  et/ou  p 


^..-«rl 


n 


Cover  title  missing/ 

Le  litre  de  couverture  manque 


Pages  discoloured,  stained         311'  a/ 
Pages  dAcolorees,  tachetAes  &■    ^/  quuas 


D 
D 


Coloured  maps/ 

Cartes  gAographiques  en  eouleur 

Coloured  ink  (i.e.  other  than  blue  or  black)/ 
Encre  de  eouleur  (i.e.  autre  que  bleue  ou  noire) 


a 


Pages  detached/ 
Pages  d^tachees 

Showthrough/ 
Transparence 


ryi    Coloured  plates  and/or  illustrations/ 
\v   I    Planches  et/ou  illustrations  en  eouleur 


a 


Bound  with  other  material/ 
Relii  avac  d'autras  documents 


n 


Quality  of  print  varies/ 
Qualita  inAgale  de  I'imprassion 

Includes  supplementary  material/ 
Comprend  du  material  supplementaire 


D 


n 


Tight  binding  may  cause  shadows  or  distortion 
along  interior  margin/ 

Lareliure  serree  peut  causer  de  I'ombre  ou  de  la 
distorsion  le  long  da  la  marge  intirieure 

Blank  leaves  added  during  restoration  may 
appear  within  the  text.  Whenever  possible,  these 
have  been  omitted  from  filming/ 
II  se  peut  que  certaines  pages  blanches  ajout^es 
lors  dune  restauration  apparaissent  dans  le  texte, 
mais.  lorsque  eela  Atait  possible,  ces  pages  n'ont 
pas  M  filmAas. 


D 
D 


Only  edition  available/ 
Seule  <kdition  disponible 

Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  ate.  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Les  pages  totalement  ou  partiellement 
obscurcies  par  un  feuillet  d'srrata.  una  pelure. 
etc..  cnt  ite  film^es  d  nouveau  de  facon  a 
obtenir  la  mailleure  image  possible 


0 


Additional  comments:/ 
Commentaires  suppldmentaires: 


Copy  has  manuscript  annotations. 

Cette  cople  a  des  annotations  manuscrltes. 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  filmA  au  taux  de  reduction  indiquA  ci-dessous. 

10X  14X  18X  22X 


26X 


30X 


v'l 


12X 


1SX 


20X 


24X 


28X 


32X 


Th*  copy  filmed  h«r«  hu  b—n  r«produe«d  thanks 
to  tho  gonorooity  of: 


L'oxomplairo  film*  fut  roproduit  grico  i  la 
gAnirositi  do: 


University  of  Toronto 

Gerstein  Science  Information  Centre 

Tho  imagos  appoaring  horo  aro  tho  boat  quolity 
possiblo  eonsidoring  tho  condition  and  logibility 
of  tho  original  copy  and  in  Itooping  with  tho 
filming  contraot  apoeif  icationa. 


University  of  Toronto 

Gerstein  Science  Information  Centre 

Laa  imagas  suivantaa  ont  Ati  roproduitoc  avoc  la 
plus  grand  toin,  compto  tanu  do  la  condition  at 
da  la  nonatO  da  I'axamplaira  film«.  at  an 
conformitO  avoc  loa  conditions  du  contrat  da 
fllmaga. 


Original  copios  in  printod  popor  covors  aro  flimod 
beginning  with  tho  front  covor  and  onding  on 
tho  laat  paga  with  a  printad  or  illuatratad  impraa- 
sion.  or  tho  bacit  covor  whon  oppropriata.  All 
othor  originol  copioa  aro  filmod  beginning  on  tho 
first  pogo  with  o  printod  or  illustrotod  improo- 
sion.  and  ending  on  the  laat  paga  with  a  printed 
or  llluatrated  improaaion. 


Lao  oxomploiroa  originoux  dont  le  couverture  an 
popier  eat  imprimOo  sent  filmOs  on  commencant 
per  le  premier  plot  et  en  terminant  soit  par  la 
derniOre  pogo  qui  comporte  une  empreinte 
d'impression  ou  d'lllustration.  si:t  par  ie  second 
plat,  salon  le  caa.  Tous  lee  autres  axempleires 
originoux  sent  filmOs  en  commencant  par  la 
pramiAro  page  qui  comporte  une  empreinte 
d'improasion  ou  d'i!!ustrstion  et  en  terminent  per 
la  derniOre  paga  qui  comporte  une  telle 
empreinte. 


Tho  laat  recorded  freme  on  eoch  microfiche 
shall  conuin  the  symbol  — ^  (mooning  "CON- 
TINUED"), or  the  symbol  ▼  (mooning  "END"). 
whichever  applies. 


Un  doe  symbolos  suivants  apparaitra  sur  la 
derniOre  imege  do  cheque  microfiche,  seion  le 
caa:  le  symbole  -^>  signifie  "A  SUiVRE".  le 
symboie  Y  signifie  "FIN". 


Mope,  platoa.  charts,  etc..  may  bo  filmed  at 
different  reduction  retios.  Those  too  lerge  to  be 
entirely  included  in  one  exposure  are  filmed 
beginning  in  the  upper  left  hand  comer,  left  to 
right  end  top  to  bottom,  as  many  frames  ss 
required.  The  following  diagrams  illustrate  the 
method: 


Los  cartaa.  planches,  tableeux.  etc..  peuvent  Atre 
filmis  i  doe  taux  da  rOduction  diffOrents. 
Lorsque  le  document  est  trop  grend  pour  Atre 
roproduit  en  un  soul  clichO,  il  est  films  a  pertir 
do  rengie  supArieur  geuche.  do  gauche  i  droite. 
et  do  haut  en  baa.  en  prenent  le  nombre 
d'imeges  nOcessaire.  Las  diagremmes  suivants 
illustrent  la  mOthode. 


1  2  3 


1 

2 

3 

4 

5 

6 

1.0 


I.I 


Li|28      i2.5 

tit 
iU 


1^ 
136 


Hi 
■u 


IL25  III  1.4 


tSi 


I 


12.0 
1.8 

1.6 


MICROCOPY  RESOLUTION  TEST  CHART 

NATIONAL  BUREAU  OF  STANDARDS 

STANDARD  REFERENCE  MATERIAL  1010a 

(ANSI  and  ISO  TEST  CHART  No.  2) 


PHYSI()L()(a  FOR  DENTAL  STCDKNTS 


WJy 


PHYSIOLOGY 


FOR 


(g) 


DEN lAL  STUDENTS 


BY 


R.G.PEARCE,  B.A.,M.D., 

Associatt'  in  Physiology,  Western  .'epcrve  University 


AND 


J.  J.  R.  MACLEOD,  M.  B.,  D.  P.  H., 

Professor  of  PhysioloRy.   Western  Reserve  University 


HyDNlNh  Il.l.LSTKATIUSS,  ISCI.UDIS'G  TEN  COLOR  HI.ATES 


ST.  LOUIS  >"l 

('.  V.  MOSEY  COMPANY 
1915 


Copyright.  1915.  by  C.  V.  Mosby  Company 


PreHH  uf 
St.  Louis 


PREFACE. 

A  knowledge  of  the  fundaniontuls  of  huiiiHii  pliysioloKy  in 
t'sscntiHl  in  tlu'  training  of  the  dental  student,  beeause  phvHioioffy 
eonstitutes,  along  with  anatomy,  the  basie  seienee  upon  wiiieli 
ail  medical  and  snrgieal  knowledge  ih  founded:  and  dentistry  is 
a  highly  speeiali/cd  department  of  snrgieal  praetiee.  To  oper- 
ate on  the  teeth  without  knowing  something  about  the  physi- 
ology of  the  body  as  u  whole,  would  reduce  the  dentist  to  tlw 
h'vcl  of  a  craftsman  who,  although  perhaps  very  hijrhly  skilled 
in  his  technical  work,  was  yet  ijuitc  ignorant  of  the  nature  of 
th«'  machine  upon  a  part  of  which  his  work  had  to  be  done. 

Hut  there  are  also  practical  reasons  why  the  dentist  should 
be  familiar  with  physiology,  for  good  health,  and  not  good  looks 
alone,  depends  very  largely  on  sound  teeth.  The  neglect  of  this 
fact  may  cause  disturbances  in  bodily  functions  to  which,  at 
first  sight,  the  teeth  may  apparently  bear  very  h.tle  relation- 
ship; thus,  extreme  emaciation,  with  its  cons(M|uent  lowering  of 
the  normal  resistance  of  the  bmly  towards  disease  arid  infection, 
is  well-known  to  be  fre(|uently  due  to  no  other  cause  than  som-- 
abnormal  or  ;  Mujlogical  condition  affecting  the  teeth;  and,  on 
the  other  hand,  this  ver.v  condition  itself  nia.v  bci  ome  intract- 
able to  the  mo.st  skilled  dental  treatment  and  hygiene,  if  meas- 
ures are  not  taken  at  the  same  time  to  impi'ove  the  geii.ral  health. 
Although  it  is  obviously  beyond  the  i)rovince  of  the  dentist  to 
undertake  the  treatment  of  the.se  general  conditions,  yet  it  is 
most  important  that  he  should  be  sufficiently  familiar  with  the 
normal  functioning  of  the  human  body  to  bo  able  1c  recognize 
what  is  really  at  fault.  A  knowledge  of  tlic  laws  of  nutrition 
and  dietetics  must  therefore  form  a  mo.st  important  part  of  every 
course  in  dentistry,  and  these  have  received  particul.ir  attention 
in  this  book. 

The  physiology  of  the  digestive  system,  of  the  cii.'ulation  of 
the  blood  and  of  tlie  nervous  system  is  sciircely  less  iniporfant. 
The  pain  and  shwk  i)roduce(i  by  a  denial  openslion  nuiy  cause 
considerable  disturbance  in  the  action  of  the  heart  or  in  the  dis- 
tribution of  blood  in  the  bodv,  and  this  di-  iirbance,  especially 

V 


HV 


VI 


PBEPACE. 


ill  viiHvH  ill  whi(*li  tho  )i<-art  and  tlii-  hlixMi  vi'HM'Ih  arc  digcafU'd,  may 
iM-r-oiiKf  HO  prnnoiiiict'd  aN  to  render  u  eertaiii  luiiouiit  of  medical 
Nki'.l  iieeewMiry.  Or  if,  ti»  avoid  such  pain,  it  Ih>  deemed  advisublc 
to  adniiniHter  aiicHtheMia,  then  must  the  dentiHt  Im'  eoiiHtaiitly 
on  his  iniai'd  that  no  more  than  the  proper  amount  of  anesthetic 
is  given,  whieli  he  can  do  intelligently  only  hy  observing  the 
condition  of  the  nervous  ami  circulatory  systems. 

Mesides  knowing  something  about  the  physiology  of  the  body 
as  a  whole,  the  dentist  must  l)e  pnrtieularly  familiar  with  the 
local  physiology  of  the  mouth,  such  as  the  finely  coordinated 
nervous  mechanisms  involved  in  the  acts  of  mastication  and 
swallowing  and  the  secretion  of  saliva.  He  must  understand 
the  nature  of  the  sensations  of  the  teeth  and  Ituecal  mucosa,  and 
be  on  the  lookout  for  any  lesions  of  the  cranial  nerves  that  siip- 
]>ly  the  muscles  ami  other  tissues  adjacent  to  the  mouth  cavity. 

The  chemistry  of  the  saliva  has  demand* d  special  attention 
because  of  the  verv  interesting  scientific  investigations  which 
are  Ix'ing  prosecutrd  ,,'garding  the  nature  of  the  undoubted 
relationship  that  c.xisis  between  changes  in  the  salivn  and  the  in- 
cidence of  dental  caries.  To  adeipiattly  describe  tlie  present 
status  of  this  work  we  have  found  it  neces.sary  to  devote  some 
space  (in  the  second  chapter)  to  a  I'cview  of  the  main  i)hysico- 
cheinical  principles  which  may  regidate  the  reaction  and  neu- 
tralizing power  of  .saliva. 

Whenever  the  occasion  presented  itself  to  do  .so.  we  hj;ve  given 
a  brief  deseription  of  the  general  nature  of  the  diseases  in  which 
dental  involvement  is  possible. 

A  few  simple,  but  very  instructive,  laboratory  demonstrations 
ai'c  described  in  an  appendix  at  tlic  close  of  the  b(K)k.  We  have 
found  that  such  demonstrations  furni.sh  an  invaluable  aid  in 
the  teaching  of  the  subject. 

To  facilitate  a  clear  understanding  of  the  subject,  diagrams 
have  been  used  whenever  neces.sary,  ami  many  of  these  have 
been  .specially  drawn  for  the  work.  To  Prof.  T.  Wiiigate  Todd 
and  Mr  ^'  if.  Spurney,  the  authors  are  deeply  indebted  for  the 
valual       issistance  which  they  gave  in  the  prejiaration  of  these. 

H.  O.   I'EARCE. 

J.  J.  II.  M.\CLE()1). 


CONTENTS. 


INTRODUCTOIIY:     THi;:  CHEMICAL  BASIS  OK  THK  CKl.L. 

Cii.uTEB  I.  Page 


The  Scope  of  PhysloloKy— The  Physlcachemlcal  IteBlB  of  Ufe- 
The  Chemical  Basis  of  Anlm- '  Tissues— Wat  r— Protelns- 
Lipoids — Carbohydrates    


17 


ClIAPTRH   II 

THE  INFLUENCE  OF  PHYSICO-CI' ^MICAL  LAWS  ON 
PHYSIOLOGICAL    ''MCKSSHIF^       iiNZYMES. 

Propertl'  of  Crystalloids— Osmotic  Phenomena  in  Cells  Hi-ac- 
tion of  Body  Fluids— Colloids— General  Nature  of  Enzymes 
or   Ferments   ' -♦» 

ClIAPTKR   III. 

DIGESTION:    NECESSITY  AND  GENERAL  NATURE. 

Digestion  in  the  Mouth— The  Salivary  Glands— The  Nerve  Supply 
of  the  Salivary  Glands — The  Reflex  Nerve  Control  of  the  Sali- 
vary Secretion— The  Normal  Stimulus  for  Salivary  Secretion 
(Direct  and  Psychological) — General  '  unctions  of  Saliva ;!7 

ClIAITEK   IV. 

DIGESTION:     THE    CHEMISTRY    OF    SALIVA    AND    THE 
RELATIONSHIP  OF  SALIVA  TO  DENTAL  CARIKS. 

Organic  and  Inorganic  Constituents — The  Reaction  of  Saliva— The 
Method  of  Measurement  of  Neutralizing  Power  of  Saliva— 
The  Deposition  of  Tartar  and  Calculi 46 


ClIAITKR   V. 

DIGESTION. 
Mastication— Deglutition   or   Swallowing— Vomiting. 

vii 


53 


Vlll 


CONTENTS. 


Page 


ClIAITKIl  VI. 


DIGESTION:     IN  THE  STOMACH. 

Mechanism  of  Secretion  of  Gastric  Juice— The  Active  Constituents 
of  Gastric  Juice— The  Movements  of  the  Stomach— The  Open- 
i.ig  of  the  Pyloric  Sphincter — Rate  of  Discharge  of  Food  from 
the  Stomach KO 

Chapter  VII. 

DIGESTION:     IN  THE  INTESTINE. 

Secretion  of  Bile  and  Pancreatic  Juice — Functions  and  Composi- 
tion of  Pancreatic  Juice  and  Bile — Chemical  Changes  Produced 
by  Intestinal  Digestion — Bacterial  Digestion  in  the  Intestine — 
Products  of  Bacterial  Digestion — Protection  of  Mucous  Mem- 
brane of  Intestine  Against  Autodigestion — Movements  of  the 
Intestines — The  Absorption  of  Food — Resume  of  Actions  of 
Digestive  Enzymes 71 

Chai'tkh  VIII. 

METABOLISM:      ENERGY  BALANCI-:. 

Introductory— General  and  Special  Metabolism— Energy  Balance  - 
Caloric  Value  ot  Foods — Basal  Heat  Production — Influence  of 
Food,  Muscular  Work,  Atmosphere,  and  Size  of  Body 8;i 

CtlAPTEK    IX. 

METABOLISM:      THE    MATERIAL    BALANCE   OF   THE    BODY. 

Starvation-Nitrogen  Balance — Protein  Sparers — The  Irreducible 
Protein  Minimum — Varying  Nutritive  Values  of  Different 
Proteins    i»l 

ClIAl'TKK   X. 

THE  SCIENCE  OF  DIETETICS. 

The  Proper  Amount  of  Nitrogen — Chittenden's  Experiments — The 
Most  Suitable  Diet  for  Efficiency —Chemical  Composition  of 
the  Common   Foodstuffs  99 


CONTENTS. 

I 
CllAI-TKU    XI. 

SPECIAL    MKTAROLISM. 

Special     Metabolism     of     Proteins — Urea— Ammonia— Creatinin  — 
Purin    Bodies— Relative    Importance    of    Proteins.    Kats    and 
Carbohydrates  in  Metabolism  

ix 

'age 

108 

115 
U'l 

i:;i 

14(1 
147 

• 

CllAlTKIt  XII. 

SPECIAL  METABOLISM. 

Metabolism    of    Kats— Metabolism    of   Carbohydrates  -Metabolism 
of  Inorganic  Salts— Vitamines  

ClIAI'TKK   XIII. 

THE   DUCTLESS  GLANOS. 

Introduction— Thyroid  and  Parathyroid  Glands     Adrenal  Glands- 
Pituitary  Gland-  Spleen— Thymus  Gland  

CilAITKH   XIV. 

ANIMAL  HEAT  AND  FEVEU. 

Animal  Heat— Normal  Temperature — Factors  Concerned  in  Main- 
taining the  Body  Temperature— Regulation  of  Body  Tempera- 
ture—Fever   

CliAITKIi   XV. 

THE  BLOOD. 

Introduction— Physical   Properties— The  Corpuscles— Erythrocytes 
—HfBmoglobin— Enumeration   of   Blood   Cells— The   Origin   of 
the     p:rythroeytes— The     White     Cells— Leucocytes— Lympho- 
cytes—Functions  of  the   White  Cells— The   Blood    Platelets— 
The  Blood  Plasma 

CllAlTKIt   XVI. 

THE   BLOOD. 

The  Defen.sive  Mechanism  oi  the  Blood  Coagulation  of  the  Blood 
— Antibodies   in    the    Blood  -^ The    Process    of    Inflammation 
Toxins— Antitoxins  -Ehrlieh's    Side    Chain    Theory— Anaphy- 
laxis—Phagocytosis— Opsonins  

# 

CONTENTS. 

ClIAPTKR  XVII. 
THE  LYMPH. 


Page 


Lymph  Formation — Lymphagogues — Lymph  Reabsorption — The 
Movement  of  Lymph  155 

Chai'teb  XVIII. 

THE  CIRCULATION. 

Introduction — The  Heart — Anatomical  Considerations — Physiologi- 
cal Properties  of  Heart  Muscle — Character  of  Cardiac  Con- 
traction— The  Sequence  of  the  Heart  Beat— The  Action  of 
Inorganic  Salts  on  the  Heart — The  Vascular  Mechanism  of  the 
Heart — Definition  of  Terms — Events  of  the  Cardiac  Cycle — 
The  Heart  Sounds — Diseases  of  the  Cardiac  Valves 159 

Chaitkk  XIX. 

THE  CIRCULATION. 

The  Blood  Flow  Through  the  Vessels — The  Part  the  Heart  Plays— 
The  Part  the  Vessels  Play — Arterial  Blood  Pressure — p-actors 
That  Maintain  the  Blood  Pressure — Velocity  of  Blood  Flow — 
The  Return  of  the  Blood  to  the  Heart— Circulation  Time — 
The  Effect  of  the  Circulation  of  the  Blood  Itself— The  Pulsa- 
tile Acceleration  of  the  Blood  Flow — The  Pulse — The  Circula- 
tion in  the  Lungs 171 


Chapter  XX. 

THE  CIRCULATION. 

The  Influence  of  the  Nervous  System  on  the  Circulation  of  the 
Blood— The  Nervous  Control  of  the  Heart— The  Cardiac 
Nerves — Accelerator  Nerves — Inhibitory  Nerves — Interrelation 
of  Inhibitory  and  Accelerator  Nerves— The  Cardiac  Center — 
The  Cardiac  Depressor  Nerves— The  Nervous  Control  of  the 
Blood  Vessels — Vasomotor  Nerves — Vasoconstrictor  Nerves — 
Vasodilator  Nerves — Vasomotor  Reflexes — The  Effect  of  Grav- 
ity on  the  Circulation — Haemorrhage —Chemical  Control  of 
Circulation— Asphyxia— Nitrous  Oxide— Cocain  184 


CONTENTS. 


XI 


Chapter  XXI. 


Page 


THE  RESPIRATION. 

Introduction — The  Internal  Respiration— Oxidation  in  the  Tissues 
— Relation  of  Oxidative  Process  to  Muscular  Activity — Physi- 
cal Laws  Governing  Solution  of  Gases — HaBmoglobin — Rela- 
tion of  Oxygen  to  Haemoglobin — The  Mechanism  of  the  Res- 
piratory Exchange — The  Effect  of  Carbon  Dioxide  on  Oxy- 
haemoglobin — The  Exchange  of  Carbon  Dioxide 197 


Chapter  XXII. 

THE  RESPIRATION. 

The  External  Respiration — Structure  of  the  Lungs — The  Mechan- 
ism of  the  Respiratory  Movements — The  Part  the  Diaphragm 
Plays — The  Part  the  Thorax  Plays — The  Movements  of  the 
Lungs — Respiratory  Sounds — Effects  of  Respiration  on  the 
Circulation — Artificial  Respiration — Volumes  of  Air  Respired 
— Mechanism  of  Gaseous  Exchange  in  Lungs 207 

Chaptkr  XXIII. 

THE  RESPIRATION. 

The  Nervous  Control  of  the  Respiration — Reflex  Respiratory  Move- 
ments— Chemical  Control  of  the  Respiration— The  Effect  of 
Changes  in  the  Respired  Air  on  the  Respiration — Mountain 
Sickness— Ventilation — The  Voice — Mechanism  of  the  Voice — 
Speech 219 


Chapter  XXIV. 


THE  FLUID  EXCRETIONS. 

The  Excretion  of  Urine — Composition  of  Urine— Organic  Constitu- 
ents— Urea — Ammonia — Uric  Acid— Creatinin — Inorganic  Con- 
stituents— Abnormal  Constituents— The  Organs  of  Excretion 
— The  Blood  Supply  of  the  Kidney— Nature  of  Urine  Excretion 
—Micturition— The  Secretions  of  the  Skin— The  Swe;  Glands 
— The  Sebaceous  Glands — The  Mammary  Glands 229 


Xll 


C(JNTENTS. 


ClIAiTKB   XXV. 


THE  NERVOUS  SYSTEM. 


Page 


General  Nature  and  Structure  of  the  Nervous  System  in  Different 
Groups  of  Animals — Fundamental  Elements  of  the  Reflex  Arc 
— Integration  of  the  Nervous  System 23!t 

ClIAlTKH  XXVI. 

THE  NERVOUS  SYSTEM. 

Reflex  Action — Tha  Nerve  Structures  Involved  in  the  Reflexes  of 
the  Higher  Animals — The  Receptors  of  Pain.  Touch,  Tempera- 
ture— Local  Anesthesia  and  Analgesia — The  Afferent  F'iber — 
Choice  of  Paths  on  Entering  Spinal  Cord — The  Nerve  Center 
— The  Efferent  Neurone^Types  of  Reflexes — Spinal  Shock — 
The  Essential  Characteristics  of  Reflex  Action — Muscular 
Tone  and  Reciprocal  Action  of  Muscles — Symptoms  Due  to 
Lesions  Affecting  the  Reflexes -44 

ClIAPTKU  XXVII. 

THE   NERVOUS   SYSTEM. 

The  Brain  Stem — The  General  Course  and  Functions  of  the  Cranial 
Nerves,  Particularly  of  the  Fifth  and  Seventli— Relationship 
of  the  Fifth  Nerve  to  the  Teeth  and  to  Neuralgia— Referred 
Pain  Through  this  Nerve— Sensitiveness  of  the  Tooth — Tri- 
facial Neuralgia — Relationship  of  the  Seventh  Nerve  to  Bell's 
Paralysis 256 

Cll.U'TKK  XXVIII. 
THE  NERVOUS  SYSTEM:     THE  BRAIN. 


Influence  of  the  Brain  on  the  Reflex  Functions  of  the  Spinal  Cord 
— Functions  of  the  Cerebrum — Cerebral  Localization — Experi- 
mental and  Clinical  Observations — The  Sensory  Centers  -The 
Mental  Process — Aphasia — The  Cerebellum — Relationship  to 
Body  Equilibrium— The  Semicircular  Canals — The  Sympa- 
thetic Nervous  System — General  Characteristics  -The  Course 
of  Some  of  the  Most  Important  Pathways 267 


C(  )XTKNTS. 


Mil 


CllAITKR    XXIX. 

THK  SPKCIAL  SENSES:      VISION. 


Page 


Optical  Apparatus  of  the  Eye— Formation  of  I{etinal  Image  — 
(  hanges  in  the  Eye  During  Accommodation  from  Near  Vision 
—The  Function  of  the  Pupil— Imperfections  in  the  Optical 
System  of  the  Eye— Long  and  Shortsightedness— Astigma- 
tism, etc.— The  Sensory  Apparatus  of  the  Eye— The  Functions 
of  the  Retina- Blind  Spot— Fovea  Centralis— The  Movements 
of  the  Eyeballs— Diplopia— Judgments  of  Vision  -Color  Vision 
— Color  Blindness  27H 


Cll.\l'TKK   XXX. 

THE  SPECIAL  SENSES. 

Hearing— The  Cochlea— How  Sound  Waves  are  Transmitted  to 
Ihi.s  by  Tympanic  Membrane  and  Auditory  Os.sicles— Causes 
of  Deafness-Taste— Nature  of  Heceptor^  for  Taste— The 
Location  of  the  Four  Fundamental  Taste  Sensations— Rela- 
tionship Between  Chemical  Structure  and  Taste— Association 
Between  Taste,  Common  Sensation  of  Touch,  and  Smell- 
Action  of  Certain  Drugs  on  Taste— Smell— Nature  of  the  Re- 
ceptors of  Smell  (the  Olfactory  Epithelium)  —  Nature  of 
Stimulus 


III! 


Cll.\ITKK   XXXI. 

THE  MUSCULAR   SYSTEM. 

The  General  Properties  of  Muscular  Tissues— Contractability— 
Irritability— The  Simple  Muscular  Contraction -Tetanic  Con- 
traction—Effect of  Load— Elaoticity  of  Muscle  —  Chemical 
Changes  Accompanying  Contraction— Rigor  Mortit- :!im 

CiCAl'TKH   XXXII. 
REPRODUCTION. 

Fertilization — The  Accessory  Phenomena  of  Reproduction  in 
Man— Female  Organs— Male  Organs— Impregni'tion— Ovulation 
— Pregnancy — Birth   :!().■; 


APPENDIX. 

Fundamental  Demonstratiou  In  Physiology 


;itiit 


Pig 
1. 

2. 
3. 
4. 


6. 


8. 

!t. 
10. 
11. 
12. 

13. 
14. 
15. 
16. 
17. 
18. 
19. 

20. 


21. 
22. 
23. 
24. 
25. 

26. 
27. 
28. 


ILLISTHATIONS. 

I'age 
Dlalysor    27 

Cells  of  parotid  gland  showing  zymogen  granules 40 

The  nerve  supply  of  the  submaxillary  gland 41 

The  changes  which  take  place  in  the  position  of  the  root  of 
the  tongue,  the  soft  palate,  the  epiglottis  and  the  larynx 

during  the  second  stage  of  swallowing 53 

Diagrams  of  outline  and  position  of  stomach  as  indicated  by 
skiagrams   taken   on    man   In   erect   position   at   intervals 

after  swallowing  food  61 

Diagram   of  stomach   showing  miniature   stomach   separated 

from  main  stomach  by  a  double  layer  of  mucous  membrane    62 
Diagram  of  time  it  takes  for  a  capsule  containing-  bismuth 

to  reach  the  various  parta  of  the  large  intestine 80 

Diagram  of  Atwater-Benedict  Respiration  Calorimeter 86 

Dietetic  chart  (colored  plate)  104 

Cretin,  19  years  old 126 

Case  of  myxoedema   127 

Photographs  showing  before  and  after  onset  of  acromegalia 

symptoms 1,'52 

Thomas-Zeiss  HsBmocytometer  142 

Diagram  of  circulation  (colored  plate)  158 

Position  of  the  heart  in  the  thorax 160 

Generalized  view  of  the  vertebrate  heart 161 

Diagram  of  valves  of  heart 162 

Dissection  of  heart  to  show  auriculo-ventricular  bundle 165 

Diagram  showing  relative  pressure  in  auricle,  ventricle  and 

aorta   168 

Diagram  of  experiment  to  show  how  a  pulse  comes  to  disap- 
pear when  fluid  flows  through  an  elastic  tube  when  there 

is  resistance  to  the  outflow 173 

Apparatus  for  taking  tracing  of  the  blood  pressure 174 

Apparatus  for  measuring  the  arterial  blood  pressure  in  man..   176 

Jacquet   Sphygmocardiograph    181 

Pulse  tracing  made  by  sphygmograph 182 

Effect  of  stimulating  vagus  and  sympathetic  nerves  on  the 

frog's  heart  185 

Tracings  of  arterial  blood  pressure  186 

Curve  chart  203 

Diagram    of    structure    of    lungs,    showing    larynx,    bronchi, 
bronchioles  and  alveoli , . ,   207 

XV 


XVI 

Kig. 

2!t. 

:{(). 

:n. 
•■!:•. 
.'!:!. 
:'.4. 
r.b. 


,-.8. 
nit. 

40. 
41. 
4J. 
4:!. 


44. 

4."). 
46. 
47. 


48. 


4ii. 


r>(t. 


oi. 
54. 
55. 
56. 
57. 
5S. 
59. 


nAA'STR.\TiOSii. 

Page 

Thf  poHition  of  the  IiinRs  in  the  thorax I'dit 

llering'B  apcaratiiH  tor  deiiionHtraiiiiK  the  attion  of  the  respir- 
atory  pump 210 

Diagram  to  «how  nioveiiient  of  diaphragm  during  respiration  L'll 

Position  to  be  adopted  for  effecting  artificial  respiration 215 

Diagram  of  laryngoscope 225 

Position  of  tlie  glottis  preliminary  to  the  utterance  of  sound.  .   226 

Position   of  open  glottis   , 226 

The  position  of  the  tongue  and  lips  during  the  utterance  ot 

the  letters  indicated  228 

Diagram  of  the  uriniferous  tubules,  the  arteries  and  the  veins 

of  the  Itidney  (colored  plate)  2:!2 

Diagram  of  urinary  system  2'i6 

Schema  of  simple  reflex  arc  240 

Diagi.  m  of  nervous  systeu;  of  segmented  invertebrate 242 

The  simplest  reflex  arc  in  the  spinal  cord 244 

Diagram  of  section  of  spinal  cord,  hhowing  tracts 247 

Reflex  arc  through  the  spinal  cord,  in  which  an  intermediary 
neurone  exists  between  the  afferent  and  efferent  neurones 

(colored    plate)    247 

Course  of  the  pyramidal   fibers  from  the  cerebral   cortex  to 

the  spinal  cord   (colored  plate)   248 

Under  aspect  of  human  brain  257 

Vertical  transverse  section  of  human  brain 258 

Diagram  of  the  dorsal  aspect  of  the  medulla  and  pons,  show- 
ing  the   floor  of   the   fourth   ventricle   with   the   nuclei   of 

origin  of  the  cranial  nerves  (colored  plate)   260 

Diagram   to   show  areas  of   referred   pain   in   distribution   of 
fifth   nerve  due  to  affections   of  the   various   teeth    (front 

view)    (colored  plate)    262 

Diagram   to   show   areas  of   referred   pain   in   distribution   of 
fifth  nerve   due   to   affections   of   the   various   teeth    (side 

view)    (colored   plate)    264 

Cortical  centers  in  man  270 

The  semicircular  canals  of  the  ear,   showing  their  arrange- 
ment in  the  three  planes  of  space 276 

Formation  of  image  on  ret'"".  281 

Section  through  the  anterior  portion  of  the  eye 282 

A,  spherical  aberration:   B,  chromatic  aberration 285 

Errors  in   refraction   286 

Semidiagrammatic  section  through  the  right  ear 292 

Diagrammatic  view  of  the  organ  of  Corti  (colored  plate) 292 

Tympanum  of  right  side  with  the  auditory  ossicles  in  place.  .   2!i4 
Schema  to  show  the  course  ot  the  taste  fibers  from  tongue  to 
brain  296 


Page 

1'0!« 

'Bpir- 

21(» 

ation  211 

215 

22.". 

iid.  .   22« 

22« 

•e  ot 

228 

reiiiR 

2:!2 

2.!6 

240 

242 

....   244 
247 


to 


247 

248 
257 

258 


261) 


262 


264 

270 

276 
281 
282 
285 
286 
292 
292 
204 

296 


PHYSIOLOGY  FOR  DENTAL  STUDENTS 


CHAPTEK  I. 


IXTRODICTOHY:  TIIK  CHK.MICAL  HAvSIS  OF  THE  CELL. 

The  Scope  of  Physiology.— Pliy.siology  i.s  tlio  study  of  tli.' 
Iiliciioiiieiia  ot"  living  things,  just  jis  auatomy  or  morphology  is  a 
study  of  tlit'ii-  structuiv.  Tlie  study  of  auatomy  is  most  logically 
pursued  by  starting  with  the  simplest  oi-Kanisms  and  frradually 
proccediiifj  through  the  mon-  complex  f^vrms  until  nmn  is 
reached.  E.xcept  for  certain  fundamental  functions,  such  as 
nutrition,  which  are  common  to  all  cells,  this  methcMl  is  not 
the  most  suitable  one  to  pursue  in  physiology,  because  in  the  low- 
est oiganisms  all  of  the  functions  are  crowded  together  in  a  lim- 
ited number  of  cells— indeed,  it  may  be  in  one  single  cell.  It  is 
easier  to  study  a  function  when  it  is  performed  by  a  tissue  or 
org  II  that  has  been  set  apart  for  this  particular  purpose  than 
wiien  it  is  performed  by  cells  tiiat  do  many  oX\.  v  things.  Another 
reason  for  i)aying  more  attention  to  the  functions  of  higiier 
rather  than  lower  animals  is  that  the  knowledge  which  we  ac(|uire 
may  be  more  directly  applicable  in  explaining  the  functions  of 
man,  and  therefore  in  enabling  us  more  readily  to  detect  and 
rectify  any  abnormalities. 

During  the  embryonic  development  of  one  of  the  higher  ani- 
mals, a  single  cell,  the  ovum,  j)roduees  numerous  other  cells, 
which  become  more  and  more  collected  into  groups,  in  many  of 
which  the  cells  undergo  very  marked  changes  in  sha|)e  and 
structure,  or  produce  materials,  such  as  the  skeleton  or  teeth, 
which  show  no  cell  structure  whatsoever.  Thus  we  have  formed 
the  tissues  and  organs,  each  having  some  particular  function  of 

17 


I 


18 


PIIYSIOLCKiY    FOR    DKNTAI.    STl'DKNTH. 


itH  own,  althouRh  rertaiii  fuiu'tions  rt'inaiii  whicli  arc  i-oimuon 
to  all.  Ill  other  words,  as  tin-  organism  Im'coiucs  iiioit!  aiul  iiiorc 
conipli'X,  tlurc  eoiiics  to  1k>  a  division  of  labor  on  tli«  part  of  the 
cells  that  eoiiipriso  it.  The  eoiulitions  are  exactly  like  those 
which  obtain  in  the  development  of  a  community  of  men.  In 
primeval  communities  there  is  little  division  of  labor,  every  indi- 
vidual makes  his  own  clothes,  hunts  his  own  foml,  manufactures 
and  uses  his  own  implements  of  war.  but  as  civilization  b«'giii8 
to  appear,  certain  individuals  specialize  as  hunters  and  fighters, 
others  as  makers  of  clothing,  others  as  artisans.  Although,  in 
its  first  stages,  this  division  of  labor  may  be  far  from  absolute, 
for  every  member  of  the  community  must  still  fight  and  take  part 
in  the  building  of  his  hut.  yet  it  soon  tends  to  become  more  and 
more  so,  until,  as  in  the  civilized  communities  of  this  twentieth 
century  of  ours,  specialization  has  become  the  order  of  the  day. 

A  good  example  of  a  (me-celletl  animal  is  the  amaba,  which  is 
often  found  floating  in  stagnant  water,  and  which  consists  of 
nothing  more  than  a  mass  of  tissue,  or  protoplasm,  as  it  is  called, 
and  yet  this  apparently  simple  structure  can  move  from  place  to 
place,  it  can  pick  up  and  incorporate  with  its  one  substance  par- 
ticles of  food  with  which  it  comes  in  contact,  it  can  store  up  as 
granules  certain  of  these  foodstuffs,  and  get  rid  of  others  that  it 
does  not  recjuire ;  it  grows  as  a  result  of  this  incorporation,  until 
at  last  it  splits  in  two  and  each  half  repeats  the  cycle.  In  other 
words,  this  single  cell  shows  all  of  the  so-called  attributes  of  lii'e : 
movement,  digestion  and  assimilation  of  food,  growth  and  repro- 
duction. No  one  of  these  properties  is  necessarily  confined  to 
living  structures  alone,  for  some  perfectly  inanimate  bodies  may 
exhibit  one  or  other  of  them,  yet  when  all  occur  together,  we 
consider  the  structure  to  be  living. 

In  the  higher  animals,  these  functions  are  performed  by  the 
so-called  systems,  such  as  the  digestive,  the  circulatory,  the  res- 
piratory, the  excretory,  the  motor,  the  nervous  and  the  reproduc- 
tive, each  system  being  composed  of  certain  organs  and  tissues 
which  are  designed  for  the  special  purpose  of  carrying  out  some 
particular  function  or  functions.  One  function,  however,  is  com- 
mon to  all  of  tiie  organs  and  tissues,  namely,  that  of  nutrition, 


TIIK  CIIKMICAI,  BASIS  (iK  TIIK  (KM,. 


19 


wliidi  iiifliiilt's  the  pioct-sN  by  wliicli  tlio  ili^fstcd  I"(mh1  is  Imilt  up 
into  the  ])rot()|)lasiii  of  tlic  cells,  or  assimilation,  ami  tlmt  by 
which  the  rcsultiiiK  Hiibstaiic<>s  an-  broken  down  a^ain,  or  difuiH- 
siniilution.  It  is  by  these  pnM-esses  that  the  energy  of  life  is  set 
free;  the  enorj?y  hy  which  the  tissues  jiert'orm  their  fi  ■•etions, 
and  which  appears  as  bmly  heat.  Every  cell  in  the  animal  luMly 
is  therefore  a  seat  of  energy  production,  and  at  the  sanit!  time 
each  is  a  machine  for  converting  this  energy  into  some  definite 
form  of  work.  In  this  regard  the  animal  machine  is  quite  unlike 
a  steam  engine,  where  energy  liberation  occurs  in  the  furnace, 
but  conversion  of  this  to  niovenumt  occurs  in  the  pistons.  The 
furnace  and  the  machinery  of  the  animal  body  are  part  and  par- 
eel  of  the  same  structures,  and  the  digestive,  circulatory,  respira- 
tory and  excretory  systems  arc  moi-e  highly  speciali/cnl  for 
tlio.purpos«?  of  transporting  fuel,  the  oxygen  to  burn  it  and  the 
gasra  j)roduced  by  its  combu.stion  to  and  from  tiie  Hying  cell. 
These  processes  of  as.similation  and  disa.ssimilation  constitute  the 
study  of  metabolism,  the  i)raetical  side  of  wiiich  is  included  in 
the  .science  of  nutrition. 

The  Physico-chemical  Basis  of  Life. 


"With  tlie  object  of  ascertaining  to  what  extent  the  known  laws 
of  i)hysics  and  chemistry  can  explain  the  fundamental  proce.ss«>s 
that  are  common  to  all  cells,  we  must  make  ourselves  familiar, 
first  of  all,  with  the  chemical  and  ph"  <  ture  of  the  constitu- 

ents of  the  cell,  and   secondly   with  i.ysieo-chemieal   laws 

which  govern  tin-  reactions  that  take  [tiace  betwwn  these  con- 
stituents. The  same  laws  will  control  the  reactions  which  take 
place  in  the  juices  secreted  by  cells:  for  example,  in  the  ;;'>od 
and  in  the  secretions,  such  as  the  saliva. 

The  Chemical  Basis  of  Animal  Tissues.— Certain  substances 
are  found  in  every  living  cell  and  in  approximately  e(iual  quan- 
tities; hence  these  may  be  considered  the  primary  constituents  of 
protoplasm.  In  general  they  consist  of  the  proteins,  lipoids,  in- 
organic salts,  water,  and  probably  the  carbohydrates.  Protoplasm 
is  the  substance  composed  of  these  primary  constituents.    By  its 


20 


PIIVSIOLOOY  FOR   DENTAL  STfDENTS. 


ai'tivity  the  protoplasm  prtMluccs  thi-  .s^vomlnnj  constituents  of 
the  cell,  which  arc  not  the  same  in  all  ccIIm.  aiul  which  include  the 
Krnnulcs  of  pigment  or  other  matrrial,  the  mass«'s  of  nflycogi-n, 
the  kIoIiuIcm  of  fat  or  the  vesicles  of  fluid  which  are  fouml  em- 
lM'«l(led  in  the  j)rotoplasni. 

]iy  what«'ver  prwess  we  'ittempt  to  isolate  itn  constituentH,  we 
of  course  kill  the  cell,  ho  that  we  <an  never  learn  by  analyMis  what 
may  have  been  the  real  nuinner  of  union  of  these  Hubstances  in 
the  living  condition.  All  we  can  find  out  \h  the  nature  of  the 
building  material  after  the  structure  (the  cell)  into  which  it  is 
built  has  been  pulled  to  piei-es.  If  the  chemical  process  by  which 
we  disintegrate  the  cell  is  a  very  <'nergetir  one,  for  example,  com- 
bustion, we  always  find  the  elements,  carbon,  hydrogen,  nitrogen, 
oxygen,  sulphur,  phosphorus,  sotliiun,  potassium,  calcium,  chlo- 
rine, and  usually  i races  of  other  elements,  such  as  iodine,  iron, 
etc.  If  the  de(  on)  posit  ion  Ih'  less  complete,  definite  chemical 
compounds  are  obtained,  nanu'ly,  water,  proteinf,  lipoids,  car- 
boliydrates,  and  the  i)hosphates  and  chlorides  of  sodium,  potas- 
sium and  calcium.  We  shall  proceed  to  consider  briefly  the  main 
characteristics  of  each  of  these  substances  and  their  place  in  the 
animal  economy. 

Water. — This  is  the  principal  con.stituent  of  active  living 
organisms,  and  is  the  vehicle  in  which  the  absorbed  foodstuffs 
and  the  excretory  j)roducts  are  dissolved.  It  nmy  be  said  indeed 
that  protoplasm  is  essentially  an  aijaeous  solution,  in  which  other 
substances  of  vast  complexity  ai-e  suspended.  Water,  on  account 
of  its  v"»*y  uni(|ue  physical  and  chemical  properties,  is  of  prime 
impoi'tancc  in  all  physiological  reactions.  These  properties  are: 
its  chemical  inactivity  at  body  temperatures;  its  great  solvent 
power  (it  is  the  best  known  universal  solvent)  ;  its  specific  heat, 
or  capacity  of  absorbing  heat ;  and,  depending  on  this,  the  large 
amount  of  heat  which  it  takes  to  change  water  into  a  vapor — 
latent  heat  of  steam.  These  last  mentioned  properties  are  made 
use  of  in  the  higher  animals  for  regulating  the  bo<ly  temperature. 

Of  great  importance  in  the  maintenance  of  the  chemical  bal- 
ance of  the  body  are  the  electric  phenomena  which  attend  the 
solution  of  certain  substances  in  water.     This  will  be  discussed 


THE  niKMICAL  BAHIS  «>r  THE  CKl.U.  21 

later  in  connoption  with  ioiii?.atinn.  Wator  has  hIho  a  vrry  (front 
surface  toiiHlon.  It  is  this  which  ilctcrniiiics  the  hci^lit  to  which 
it  will  Hsu  in  plants  and  in  the  soil,  and  which  no  doubt  plays  a 
role  in  tho  prooessps  of  absorption  Ko'iug  on  i'l  various  parts  of 
the  animal  bo<ly. 

pR<»TKiNs. — Th«'  jfrcat  importance  of  proteins  in  animal  life  is 
att«'(*te<l  by  the  fact  that  they  are  absolutely  indis|>ensable  in- 
Rredients  of  food.  An  animal  fed  on  food  containiiiK  no  protein 
will  die  nearly  as  soon  as  if  foo<l  had  Ihm-h  withheld  altoifether. 
Proteins  are  complex  bodies  composed  of  carbon,  hydrogen,  oxy- 
l?en,  nitrogen,  and,  in  nearly  all  caoes,  sulphur.  S' .  e  may  con- 
tain in  addition  phosphorus,  iron,  io<line,  or  certain  other 
elements.  The  proportions  in  whi«'h  the  alM)ve  elements  are 
found  in  different  proteins  do  not  vary  so  much  as  the  ditTereiices 
in  the  chemical  behavior  of  the  prot^-ins  would  lead  us  to  expect. 
In  Kenerul  the  percentage  com,';sition  by  weight  is: 

Carbon S'J    per  cent 

Hydrogen 7    per  cent 

Oxygen 22    per  cent 

Nitrogen   16    per  cent 

Sulphur 1  to  2  per  cent 

The  essential  differences  in  tho  structure  of  the  molecules  of 
different  proteins  have  b«»en  brought  to  light  by  studies  of  the 
products  obtained  by  partially  splitting  up  the  molecule.  We 
are  able  to  do  this  by  subjecting  protein  to  the  action  of  super- 
heated steam,  or  by  boiling  with  acids  or  alkalis's  in  various  con- 
centrations, or  by  the  action  of  the  ferments  of  digestive  juices 
or  by  bacteria.  The  cleavage  i)roduced  by  ferments  or  bacteria 
is  much  more  discriminate  than  that  brought  about  by  strong 
chemical  reagents;  that  is  to  say.  the  chemical  groupings  are  not 
so  roughly  torn  asunder  by  the  biological  as  by  the  chemical 
agencies. 

M  first  the  proteins  break  \i\}  into  eompounds  still  i)os.sessiiig 
many  of  tiie  features  of  the  i)rotein  molecule.  These  are  the 
proteoses  and  peptones,  and  they  consist  of  aggregates  of  smaller 


•)•> 


PHYSIOLOGY  FOB  DENTAL  STUDENTS. 


molecules,  which  can  be  further  resolved  into  simple  crystalline 
substances.  These  have  boon  callod  the  building  stones  of  the 
protein  molecule,  and  altliough  llioy  differ  from  one  another  in 
many  respects,  they  have  one  feature  in  common,  namely,  that 
each  consists  of  an  organic  acid  liaving  one  or  more  of  its  hydro- 
gen atoms*  substituted  by  the  radicle,  NIL.  Such  substances  are 
called  amino  bodus.  For  example,  the  formula  of  acetic  acid 
is  CILCDOn.  If  for  one  of  the  11  atoms  there  is  substituted  the 
NIL  group,  wo  luivc  CII,NILCOOII,  which  is  amiini  acetic  acid, 
or  glycine.  Tlie  same  sort  of  substitution  may  take  place,  not 
alone  in  the  simple  organic  acids  containing  one  acid  group,  but 
also  in  those  containing  two  acid  groups,  as  in  amino-succinic 
acid,  coon.  CIL (NIL) coon,  or  in  acids  containing  the  aro- 
matic or  benzene  ring  group,  as  in  the  case  of  tyrosine, 
C,.,H40H.  C,H,.  NIIoCOOII,  or  again  there  may  be  two  amino 
acid  groups  present,  as  in  the  diamino  acid,  ornithin  or  diamino- 
valeric  acid,  C,IL(NlL)X"OOII. 

That  the  large  aiid  complex  protein  molecule  is  really  built  up 
out  of  these  amino  bodies  lias  boon  very  conclusively  shown  by 
Eniil  Fischer,  wlio  suecoodod  in  causing  two  or  more  of  tiiem  to 
become  united  to  form  a  body  called  a  j^oh/pcptid.  When  sevoral 
amino  bodies  were  thus  synthesized,  the  polypeptid  was  found  to 
possess  many  of  the  pi-<)i)ortios  of  peptones,  which  we  have  just 
stated  are  the  earliest  decomposition  products  of  protein. 

Proteins  differ  from  one  another,  not  only  in  the  nature  of  the 
amino  bodies  of  which  tlit  y  are  composed  (although  certain  of 
these  are  common  to  all  proteins),  but  also  in  the  manner  in 
which  the  amino  bodies  are  linke<l  together.  We  shall  see  the 
practical  value  of  knowing  what  are  the  amino  bodies  in  a  given 
protein  whon  wo  oomo  to  tlio  subject  of  diototics  (see  p.  i>!M. 

The  proteins  of  the  cell  are  classified  into  two  groups.  The 
first  includes  the  simple  i)roteins,  such  as  egg  and  serum  albumin  ; 
and  the  second,  the  compound  proteins,  from  which  non-protein 
groups  can  bo  split  off.  As  i)riiiijiry  coll  oonstituonts,  the  follow- 
ing siiiii>lo  ami  compound  protoins  are  important :  albumin, 
globulin,  nuoleoprotoin,  ami  tlu;  glycoproteins.  They  are  all  of 
the  nature  of  colloidal  substances  (see  p.  .'52),  and  therefore  are 


THE  CHEMICAL  BASIS  OP  THE  CELL. 


23 


either  precipitated  or  coagulated  when  solutions  containing  them 
are  boiled  or  have  inorganic  sjilts  dissolved  in  them. 

Albumins  are  characterized  chiefly  by  their  great  solubility  in 
water.  Three  forms  are  of  importance :  egg  albumin,  lactal- 
bumin  of  milk,  and  serum  albumin. 

Globulins  occur  principally  in  the  muscle  proteins,  and  arc 
insoluble  in  water,  but  soluble  in  dilute  neutral  salt  solutions. 
Jlany  consider  that  the  albumins  and  globulins  are  only  nutri- 
tive materials  from  which  the  protoplasm  manufactures  the 
compound  proteins  which  are  the  essential  cellular  proteins. 

Xuclcoprotcins,  both  in  (juantity  and  in  relation  to  their  activ- 
ity, are  probably  the  most  important  constituents  of  the  cell. 
They  have  a  very  comi)le.x  structure,  and  occur  in  many  varieties. 
They  consist  of  a  combination  between  protein  and  a  substance 
called  nucleic  acid,  which,  on  being  broken  up  by  chemical 
means,  yields  phosphoric  acid,  a  simple  sugar  called  pentose,  and 
nitrogenous  substances  known  as  purine  bases,  and  pyrimidines. 
The  purine  bases  are  of  great  interest,  because  they  are  the  ante- 
cedents in  tile  body  of  uric  acid,  which,  being  relatively  insolubh'. 
may  become  deposited  from  the  bwly  fluids  and  cause  gout  or 
gravel.  That  it  is  possible  to  have  an  enormous  variety  of  nucleo- 
proteins  can  be  imagined  wlien  we  consider  that  there  exist  differ- 
ent sorts  of  purine  ba.s(»s,  of  carbohydrates,  and  of  amino  bodies. 
The  nucleus  of  the  cell  contains  a  nucleoprotein  which  is  particu- 
larly rich  in  purin  bases  and  is  often  called  nuclein. 

Phosphoproteins  are  compounds  of  phosphoric  acid  and  simple 
proteins,  without  any  nucleic  acid.  An  example  is  the  casein  of 
milk  {.see  j).  105). 

Gli/coprufi'ins  are  compound  of  carbohydrates  with  proteins. 
The  mucin  of  saliva  is  an  example  (see  p.  -46). 

Insolubh  proteins  resemble  the  coagulated  proteins,  and  are 
left  behind  after  tlie  extraction  of  the  other  proteins  from  the 
cell. 

•liii>()M)s. — These  include  all  tlie  substances  composing  a  cell 
whicli  are  soluble  in  fat  solvents.  Hesides  fats  an<l  fatty  aeitls. 
the  most  important  of  these  sub-stances  are  lecithin  and  choles- 
terol. 


24 


IMIYSIOUXJY    FOR   DENTAL    STUDENTS. 


LiiithiH  is  widely  listributi'd  in  the  animal  body,  and  is  very 
important  in  the  metabolism  and  in  the  j)liysieal  strueture  of  the 
cell.  It  ponsi.sts  chemieally  of  glycerine,  fatty  acid.  phosi>horic 
acid,  and  a  nitrogenous  base  called  cholin. 

Choli alirol  is  another  widel.v  distributed  lipoid.  It  is  not  in 
reality  a  fatty  body,  but  i'ath«'r  resembles  the  terpcues.  Leeitliin 
anil  cholesterol  are  abundant  in  brain  tissue,  in  the  envelopes  of 
erythrocytes,  and  in  bile. 

Th<  fats  exist  mainly  as  secondary  con.stituents  of  the  cell, 
being  dei)osited  in  very  large  amounts  in  certain  of  the  connective 
tissue  cells  of  the  bmly.  in  bone  nuirrow  and  in  the  omental  tis- 
sues. Chemicall.v.  the  tissue  fats  are  of  three  kinds:  olein.  pal- 
mitin,  and  stearin,  each  having  a  distinctive  melting  point.  They 
are  compounds  of  the  tri-valent  alcohol,  glycerine,  and  one  of  the 
higher  fatty  acids,  oleic,  palmitic,  or  stearic  acid.  Besides  those 
that  arc  present  in  the  animal  tissues,  fats  made  up  of  glycerine 
coiJibined  with  various  lower  members  of  the  fatty  acid  scries 
occur  in  such  secretions  as  milk.  In  order  to  understand  the 
influence  which  fats  have  on  general  metabolism,  it  is  important 
to  remember  that  they  differ  from  the  carboiiydrates  in  contain- 
ing a  very  low  |)ercentag»>  of  oxygen  and  a  relatively  high  ])er- 
centage  of  hydrogen  and  carbon.  Thus,  the  empirical  formula 
of  palmitin  is  <'o,II,,..0,,  or  r,n.((',eH.n( ).").;.  that  of  dextrose 
C«H,,0„.  and  of  protein  r,,H,,„X,sO,„S. 

The  Carbohydrates  are  also  mainly  secondary  cell  constitti- 
ents.  although  it  is  becoming  more  and  more  evident  that  they 
are  also  neces.sary  as  primary  constituents.  In  general  they  ma.v 
l>e  defined  chemically  as  consisting  of  the  elements  (_',  II,  and  <>, 
the  latter  two  being  present  in  the  molecule  in  the  same  proj)or- 
tion  as  in  water;  thus,  the  fornuila  for  dextrose  is  C,,!!,^.!),;. 

The  basic  carbohydrates  arc  the  simple  sugars  or  motiosat- 
charidis,  .such  as  grape  sugar  or  dextrose.  When  two  molecules 
of  monosaccharide  become  fused  together  with  the  elimination 
of  a  molecule  of  water  (tliiis  giving  the  formula  <\_,ir,_.(),,),  a 
secondary  sugar  or  disaccharide  lesulls.  ("ane  sugar,  lactose  (or 
milk  sugar)  aiul  maltose  (or  malt  sugar)  are  <'xamples.  If  sev- 
eral nonsaccharide  molecules   similarly    fuse   together,    polysav- 


THK  CHEMICAL  HASIS  OK  TIIK  CKI.L. 


25 


c^ iirkhs  liHviiig  the  formula  (C,iIT,„0.)„  arc  forint-il.  Those  in- 
I'lude  the  dcxtrincs  or  gums,  glycogon  or  animal  stai-ch,  the  ordi- 
nary starches,  and  cellulose.  Since  so  many  molecules  are  fused 
together,  it  is  not  to  be  wondered  at  that  there  should  be  so  nmny 
varieties  of  «'ach  of  these  classes  of  polysaccharides,  for,  as  in  th(( 
case  of  proteins,  not  only  may  the  actual  ''building  stones"  of 
the  molecule  be  diffei-ent,  but  tiiey  may  be  built  together  in  very 
diverse  ways.  The  polysaccharides  may  lu'  hydrolyzed  ( i.  e., 
caused  to  take  up  water  and  split  up)  into  disaccharides,  and 
these  into  monosacchariilcs  by  boiling  witli  acids  or  by  tiie  action 
of  diastatic  and  inversive  ferments  (see  [).  -Hi). 


CHAPTER  II. 

THE    INFLUENCE   OV   PHYSICO-CHEMICAL    LAWS    ON 
PHYSIOLOGICAL  PROCESSES:    ENZYJIES. 

Having  Icaniod  of  wliat  niatorials  tlio  ecll  is  coinposod,  wo  may 
proceed  to  cn(|uire  into  the  clioniical  and  physical  reactions  by 
wliich  it  performs  its  functions.  Tiie  cell,  eitiier  of  plants  or 
of  animals,  i'  v  be  considered  as  a  ciieinical  laboratory,  in  which 
definite  reac  iis  are  constantly  jjoing  on,  being  guided,  as  to 
their  direction  and  scope,  by  the  piiysical  conditions  under  which 
they  occur.  A  study  of  the  material  outconit;  of  tluse  reactions 
constitutes  the  study  of  metabolism,  to  which  special  chapters 
are  devoted  further  on.  At  ])resent,  however,  we  must  briefly 
examine  the  j)hysico-ehemical  conditions  exi.sting  in  the  cell 
vvhieh  may  give  tiie  directive  influence  to  the  reactions.  Wiiy 
should  certain  cells,  like  those  which  line  tiie  intestine,  absorb 
digested  food  and  pass  it  on  to  the  bloo<l,  whilst  others,  like  thust- 
of  the  kidney,  i)ick  up  the  effete  j)roduets  from  the  blood  and 
e.xcrete  them  into  the  urine?  We  must  a.scertain  whether  these 
arc  processes  depending  on  purely  physico-chemical  causes,  or 
whether  they  are  a  function  of  the  living  protoplasm  itself,  a 
vital  action,  as  we  may  call  it.  In  general  it  may  be  said  that 
the  aim  of  most  investigations  of  the  activities  of  cells  is  to  find 
a  physico-chemical  explanauon  for  them,  and  it  is  one  of  the 
achievements  of  modern  physiology  that  some  should  have  been 
thus  explainable.  A  large  niunber,  however,  do  not  permit  of 
swell  an  explanatioji,  and  tiiis  has  induced  certain  investigatoi-s 
to  believe  that  there  are  some  animal  functions  which  are  strictly 
vital  and  can  never  be  explained  on  a  physical  basis.  The  "phys- 
ical" and  the  "vital  scliools"  of  physiologists  are  therefore 
always  with  us. 

From  the  .standjtoint  <>(  physical  chemistry,  the  cell  may  be 
considered  as  a  collection  of  two  classes  of  chemical  substances, 


CRYSTALLOIDS. 


27 


called  crystalloids  and  colloids,  dissolved  in  water,  in  the  lipoids, 
or  in  each  other,  and  surrounded  by  a  membrane  which  is  per- 
meable towards  certain  substances  but  not  towards  others  (semi- 
permeable, as  it  is  called).  On  a  larger  scale,  the  same  general 
conditions  exist  in  all  of  the  animal  fluids,  such  as  the  blood,  the 
lymph,  the  secretions  and  the  excretions,  so  that  we  may  stu«ly 
the  laws  with  a  view  to  applying  thorn  to  both  cells  and  body 
fluids. 

Properties  of  Crystalloids.— As  their  name  implies,  these 
form  crystals  under  suitable  conditions.  When  i)resent  in  solu- 
tion they  diffuse  quickly  tlirougiiout  the  solution,  and  can  readily 


Kit;.  I. — Kiiilyscr  mailc  nf  tul>c  of  imrohnu'iit  paiicr  suspfiulcii  in  a  vfs.scl 
iif  distilled  wattT.  The  fluid  to  be  dialyscd  is  rilaced  In  the  tul)e,  and  the 
distillfd   water   must   be   fiequ- ntly  changed. 


pass  t^'-ough  membranes,  such  as  a  piece  of  parchment,  placed 
hoU  le  solution  containing  thtm  and  another  solution.   This 

prot  ,  called  diaf  •  •,  and  tiie  apparatus  used  for  observing 

it,  a  iimujarr  (see  Fig.  1).  Dialysis  differs  from  filtration,  tiie 
latter  process  consisting  in  the  pa,s.sage  of  fluids,  and  the  sub- 
stances dissolved  in  them,  thi'ough  more  or  less  pervious  mem- 
branes as  a  result  of  differences  of  pressure  on  tlie  two  sides  of 
the  membrane.  If  instead  of  using  a  simple  membrane,  such  as 
l>archment,  we  choose  one  which  does  not  i)ermit  the  crystalloid 
itself  1o  diffuse,  but  permits  the  solvent  to  do  .so — a  simiix  rmcnhir 
mnnhrtinc,  as  it  is  called, — a  very  interesting  property  of  dis- 
solved cry.stalloids  comes  to  light,  namely,  their  teudem^y  to  ex- 


L'8 


lMIVsl(»l,»XiY    FOR   DENTAL   STUDENTS. 


jmiid  in  the  solvci'.t,  that  is,  to  take  up  morp  room  by  attracting 
the  solvent  through  the  membrane.     Cell  membranes  are  semi- 
permeable, but  they  are  too  small  and  delicate  for  experimental 
jturposes,  for  which  we    use   one   compoH<'d  of  a  precipitate  of 
copper  ferrocyanidc  supported  in  tlie  pores  of  an  unglazcd  clay 
vessel.    If  a  solution  of  a  crystalloid — say.  cane  sugar — be  placed 
in  such  a  vessel  and  tins  then  submerged  in  water,  it  will  be  found 
that  the  cane  sugar  solution  (|uickly  increases  in  volume,  or,  if 
tliis  be  preventtnl  by  closing  uj)  the  vessel  and  connecting  a  pres- 
sure gauge  with  it.  a  remarkably  high  pressure  will  become  devel- 
oped.   Tills  is  called  osmotic  prfssun,  and  it  is  a  measure  of  the 
tendency  of  dissolved  crystalloids  to  expand  in  the  solvent.     It 
has  been  found  that  the  laws  which  govern  osmotic  pressure  are 
identical  with  those  governing  the  behavior  of  gases.    Therefore, 
the  osmotic  pressui-e  would  be  expected  to  be  proportional  to  the 
iuunber  of  molecules  of  tiissolved  crystalloid  and  such  is  the  case 
for  the  sugars,  but  it  is  not  .so  for  the  saline  crystalloids,  such  as 
the   alkaline   chlorides,    nitrates,   etc.      These   cause   a   greater 
osmotic  pressure  tiiaii  we  should  expect   from  their  molecular 
weights.   Why  is  this?   The  answer  to  the  ((uestion  is  revealed  by 
olwerving  the  behavioi-  of  the  two  classes  of  crystalloids  towards 
tln'  electric  current.    Solutions  of  sugars  or  urea  do  not  conduct 
the  current  any  better  than  water,  whereas  .solutions  of  saline 
crystalloids  conduct   very   readily.     The   former  are   therefoi-e 
called  tion-fhclrohjf(s  and  the  latter  dectroh/tfs.    The  reason  for 
these  differences  has  been  found  to  be  that  molecules  of  electro- 
lytes when  they  are  dissolved  break  into  parts  called  "ions," 
and  each  ion  carries  a  charge  of  electricity  of  a  certain  sign,  i.  e., 
positive  or  negative.     Whenever  an  electric    current    is   passe«l 
througti  the  .solution,  the  ions,  hitherto  distributed  througimut 
tile  solution  in  pairs  carrying  charges  of  opposite  signs,  now  line 
themselves  up  so  that  the  ions  with  one  kind  of  electrical  charge 
form  a  chain  across  the  solution  along  wiiicli  that  kind  of  elec- 
tricity  r<'adily  pas.ses,  and  in  so  doing  carries  the  ions  with  it. 
This   .splitting  of  ebvirolytes  into  ions  is  called  (lissorintioii  or 
iotnzation.    The  ions  which  carry  a  charge  of  positive  electricity 
and  which  tiierefore  travel  towards  the  kathode  or  negative  jiole 


CRVSTAM.(ims. 


29 


(since  uiilik»;  t'li'ctricitii'S  attract  caeli  other)  are  eall<>tl  kalhions, 
ami  the  nepitively  eliarjjed  ions  tliat  travel  to  tl»e  ano<le,  anions. 
Hydrogen  and  the  nietullie  elements  belong  to  the  group  of 
kathioiis;  oxygen,  the  halogens  and  all  aeid  groups,  to  the  anions. 
Tliese  facts  may  be  more  clearly  understood  from  the  following 
ei|uations: 

In  water,  or  in  a  solution  of   a   non-electrolyte,    molecules   of 
II^O  or  non-electrolyte  exist  thus: 

ILO  II„0  H„0 

ILO  11,0  ILO 

ILO  H„0  ILO 

In  a  solution  of  an  electrolyte,  the  molecules  s])lit  into  ions 
thus: 

Na*     CI-  Na*     CL     Na*     ('L 

Nu^  CI-     Na^     Cl~      iNV     CV 

Na*     CI  Na^     CL     \a^     VI 

Wlien  an  electric  current  presses  through   a   solution   of  an 
electrolyte,  the  ions  arrange  themselves  llms: 


Kathode" 


Anode* 


Na* 

Na* 

Na* 

ci- 

ci- 

ci- 

Na^ 

Na* 

Na* 

ci- 

ci- 

ci- 

i\a* 

Na* 

Na* 

ci- 

ci- 

ci- 

To  return  to  osmotic  jjressure,  the  ions  influence  this  as  if  they 
were  molecules,  so  that  when  we  dissolve,  say,  so<lium  chloride 
in  water,  tiie  osmotic  pressure  is  almost  twice  what  it  should  be. 
because  every  molecule  has  split  into  two  ions. 

Osmotic  Phenomena  in  Cells. — Over  and  over  again  we  shall 
have  to  refer  to  these  physico-chemical  processes  in  explaining 
physiological  phenomena.  For  the  present  it  may  make  matters 
clearer  if  we  consider  how  osmosis  explains  the  behavior  of  ccVs 
irhni  suspcndrd  in  diffennt  solutions.  The  cell  wall  acts  as  a 
semipermeable  membrane.  Thus,  if  we  examine  red  blood  cor- 
puscles suspended  in  different  saline  solutions  under  the  micro- 
scope, we  shall  observe  that  they  shrink  or  crenatc  when  the  solii- 


;m 


PIIYSI()I,(Miy    F'lK    DKNTAI,    S^TIDKNTS. 


tloiwarc  HirnuK,  iiiul  cxi.iin.l  and  become  fjlohiilai-  in  .sluip.'  wln-n 
these  an;  weak.  Tlio  .shrinkaK"'  is  .liic  to  ditrusion  of  water  out 
of  the  corpusclo  and  tlu>  swdlinjf.  to  its  diffusion  in;  tiiat  is  to 
say,  in  the  former  ease  the  osniotie  pressure  of  the  surroun<liiig 
fluid  is  greater  than  that  of  the  eorpuseular  eontents  and  vhr 
versa  in  the  latter  ease.  In  this  way  we  have  a  siniph'  and  eon- 
venient  method  of  eomparing  the  relative  osmotie  pressure  of  dif- 
ferent solutions.  Wlien  the  solution  has  a  higher  jjressure.  it  is 
ealled  hypcriouk,  when  less,  hypotonic,  when  same,  isotonic. 
It  is  evident  that  the  body  fluids  must  always  be  isotonic  with  tlie 
eell  contents,  and  that  we  must  be  earefiil  never  to  intro«luee 
fluids  into  the  blood  vessels  that  are  not  isotonic  with  tlie  blood. 
A  one  per  cent  solution  of  common  salt  is  almost  isotonic  with 
blood,  and  is  accordingly  used  for  intravenous  or  .subcutaneous 
injections,  or  for  washing  out  bo<ly  cavities  or  surfaces  lined  with 
delicate  membranes,  such  as  the  conjunctiva  or  nares. 

Reaction  of  Body  Fluids.— Closely  dependent  upon  tlx'se 
properties  of  ionization  are  the  reactions  which  determine  the 
acidity  and  alkalinity  of  the  body  fluids.  When  we  speak  of  the 
degree  of  acidity  or  alkalinity  of  a  solution  in  chemistrv,  we 
mean  the  amount  of  alkali  or  acid,  respectively,  which  it  is  nec- 
es.sary  to  add  in  order  that  the  solution  may  become  neutral  to- 
wards an  indicator,  such  as  litmus.  This  titrible  reaction  is  how- 
ever a  very  different  thing  from  the  real  strength  of  the  acid  or 
alkali ;  for  exami)le,  we  may  have  solutions  of  lactic  and  hydro- 
chloric acids  that  require  the  same  amount  of  alkali  to  neutral- 
ize them,  but  the  hydrochloric  acid  solution  will  have  much  more 
powerful  acid  properties  (attack  other  substances,  taste  more 
acid,  act  much  more  powerfully  as  an  antiseptic,  etc.).  The  rea- 
son for  the  difference  is  the  degree  of  ionization  ;'  the  strong  acids 
ionize  much  more  completely  than  the  weak.  As  a  result  of  this 
ionization,  each  molecule  of  the  acid  splits  into  H-ions  and  an 
ion  composed  of  the  remainder.  To  ascertain  the  real  acidity 
ive  must  therefore  measure  the  concentration  of  H-ions.  (These 
con.siderations  also  apply  in  the  case  of  alkalies,  only  in  this  case 
Oll-ions  determine  the  degree  of  alkalinity.)  This  can  be  done 
accurately  by  measuring  the  speed  at  wiiich  certain  chemical 


HKACTION    (IK    I«IH>Y    KI.I  1I>S. 


31 


proi'OSKt's  piocffd,  tliat  drpciul  on  llic  coiu'ciitnitioii  of  Il-ioiis. 
The  convci-sioii  of  cane  supar  into  invert  sii^jar  is  a  wood  priM-esM 
to  employ  for  measuring  tlie  speed  of  reaction. 

But  even  this  refinement  in  teelini(pie  dws  not  enable  us  to 
measure  the  II -ion  concentration — for  now  we  must  use  tins  ex- 
pression when  speakinp  of  aeidity  or  alkalinity — of  such  impor- 
tant fluids  as  blood  and  salini,  in  whieh  there  is  an  extremely 
low  H-ion  concentration.  If  either  of  these  fluids  be  jdacwl  on 
litmus  papers,  the  red  litmus  turns  blue,  but  all  that  this  sifjnifies 
is  that  the  litmus  is  a  stronjjer  acid  than  those  present  in  blood 
or  saliva,  so  that  it  decomposes  the  bases  with  which  tht-y  were 
combined  and  changes  the  color.  If  we  emi)loy  i)henolphthalein, 
which  is  a  much  fwbler  acid,  then  blood  serum  reacts  neutral  and 
saliva  often  acid. 

There  are  two  methods  open  to  us  for   measuring  the   Il-ion 
concentration  in  such  cases: 

1.  The  Iljjdrojjot  Ehitrode. — Place  the  fluid  (e.  g.,  blood 
serum  or  saliva)  in  a  snuiU  closed  vessel  filltMl  with  hydrogen  ami 
with  a  platinum  electrode  dipping  into  it.  Connect  this  hydro- 
gen electrode  with  a  standard  calomel  eleetro«le  by  wires  in  the 
course  of  which  are  suitably  arranged  electrical  instruments  for 
the  measurement  of  electromotive  force.  From  the  ditferencc  in 
the  electromotive  force  which  is  found  to  exist  between  the  hydro- 
gen and  the  calomel  electrodes,  we  can  calculate  the  H-ion  con- 
centration. This  method  is  being  employed  for  measuring  the 
reaction  of  saliva  in  relationship  to  its  influence  on  caries  of  the 

teeth. 

2.  The  Use  of  Standanlized  Indicators. — It  has  been  found 
that  different  indicators  change  color  at  different  H-ion  concen- 
trations. Hy  taking  solutions  with  variable  known  proportions 
of  acid  and  alkaline  salts  such  as  NhIIoPO^  and  NaoIIP04  or 
NallCOj  and  measuring  their  actual  acidity  in  terms  of  the 
H-ion  concentration — by  the  electi'ical  method — and  then  observ- 
ing their  behavior  with  different  indicators,  it  has  been  possible 
to  e\'aluate  the  different  indicatoi*s  in  terms  of  the  H-ion  concen- 
tration at  which  they  change  color.  Expressing  the  results  as  the 
fraction  of  a  normal  solution   of  H-ion   at  which  this  change 


32 


•IIVsKIMMiy    KilR    DKNTAI,    STCDENTS. 


I 


(M-eiirs.  it  has  lictii  foiiiul  that  iiaiaiiitro-iilit'iiol  turns  at  about 
.000.001  (or  1  X  10  "  I,  which  is  the  ll-ioii  foiicfiit ration  of  [lurc 
water,  and  is  thcrcfoii-  the  most  |»nictical  |)oint  to  chooso  as  iinli- 
catiiiR  neutrality.  .Methyl  red  and  rosolie  aeid  also  change  color 
about  this  ])oiiit.  Phenolpiitlialeiii.  on  the  other  hand,  changes 
color  at  a  11-ion  concentration  of  1  .\  10  ',  i.  e.,  its  is  very  sensitive 
towards  acids,  and  methyl  orange,  at  1  .\  10-^,  i.  e.,  it  is  relatively 
insensitive  towards  acids. 

The  indicators  wliich  ciiange  color  at  about  the  Il-ion  concen- 
trations found  in  animal  fluids  are  rosolie  acid,  paranitrophcnol 
and  methyl  red.  \\y  comi)arinR  the  color  prwluccd  by  adding 
one  of  these  indicators  to  the  unknown  fluid  with  those  obtained 
by  adding  the  same  indicator  to  a  series  of  .solutions  containing 
varying  but  known  Il-ion  concentrations,  we  can  accurately  tell 
the  Il-ion  concentration  of  the  unknown  solution,  for  the  Il-ion 
concentration  of  the  solution  whose  tint  matches  with  that  of  the 
unknown  is  the  Il-ion  concentration  of  the  latter.  The  series  of 
.standard  solutions  is  nuulc  by  mixing  varying  proportions  of  acid 
and  alkaline  phosphates. 

Before  leaving  this  sub.ject.  it  is  important  to  point  out  that 
the  blootl  lias  an  Il-ion  concentration  wliich  is  jiractically  the 
.same  as  that  of  water,  i.  e.,  is  as  nearly  neutral  as  it  could  be.  It 
also  has  the  power  of  maintaining  this  neutrality  practically  con- 
stant even  when  large  amounts  of  acid  or  alkali  are  added  to  it. 
Although  saliva  and  .some  other  Ixxly  fluids  sire  not  .so  nearly 
neutral  as  blood,  yet  they  can  also  lock  away  much  acid  or 
alkali  without  materially  changing  the  Il-ion  concentration.  This 
property  is  due  to  the  fact  that  the  body  fluids  contain  such  salts 
as  phosphates  and  carbonate's,  which  exi.st  as  neutral  and  aeid 
salts,  and  can  change  from  the  one  state  to  tlie  other  without 
greatly  altering  the  Il-ion  concentration,  and  yet.  in  so  changing, 
can  lock  away  or  liberate  II-  or  Oll-ions.  This  has  been  called 
the  "buffer"  action,  and  is  a  iiip.st  important  factor  in  maintain- 
ing constant  the  neutrality  of  the  animal  body. 

Colloids. — These  are  substances  which  do  not  diffuse  through 
membranes  when  they  are  dissolved.  Thus  if  bloml  scrum  be 
placed  in  a  dialyser  which  is  surrounded  by  distilled  water,  all 


rot,M»ins. 


33 


tlic  prystalloiils  will  (litTuHt-  out  of  it.  Ifiivinn  tin-  <'ollt)i(ls,  wliicli 
(•onsist  iiiHiiily  of  prott-iiis.  The  physicjil  rciisoii  for  this  failure 
to  (lifTiiMt*  is  tli<>  larK*'  ^i/-*'  <>f  tin'  inolfciilcs,  in  coinparison  with 
till'  small  si/c  of  those  of  thf  crystalloids.  My  caiisiiiu  a  hfaiii  of 
liffht  to  jmss  through  a  colloitlal  solution  and  holding  a  iiiicro- 
scopc  at  rifjlil  an^jlcs  to  this  licain.  the  i-olloidal  partii'h-s  Im-comm' 
<'vi«lt'nt,  just  as  particlis  '•♦"  dust  hi'conit'  evident  in  Uw  air  of  a 
room  in  a  beam  of  daylight.  In  eontirmation  of  this  view  of  the 
cause  of  the  indilfusihility  of  colloiils  is  the  fact  that  filters  can 
Im'  made  of  un^la/.cd  porcelain  impregnated  with  (;elatin.  in 
which  the  pores  are  then-fore  very  minute,  through  which  col- 
loids cannot  pass,  though  water  and  inorganic  salts  do  so.  When 
l»l(H)d  .serum  is  filtered  through  such  a  filter,  tln'  filtrat*-  contains 
no  trace  of  protein.  The  colloidal  molecules  can  also  very  readily 
be  caused  to  fuse  together,  thus  forming  aRgrejiates  of  molecules 
which  become  so  larjjc  that  they  either  confer  an  opacity  on  the 
solution  or  actually  form  a  precii>itate. 

This  fusinjr  together  of  colloidal  particles  can  be  brought  about 
either  by  adding  certain  neutral  salts  or  by  mi.xing  with  certain 
other  colloids.  The  ex])lanation  of  these  results  is  as  follows: 
colloidal  molecules  carry  either  a  positive  or  a  ne(^..tive  electrical 
charge,  and  when  this  is  neutralized,  the  colloidal  molecules  fuse 
together,  i.  e.,  become  aggregated.  This  neutralization  of  elec- 
trical charge  can  be  brought  about  either  by  adding  an  t'lectro- 
'.vte.  one  of  whose  ions  will  supply  the  proper  electrical  chui'ge, 
or  by  a  colloid  having  an  opposite  charge.  Tlnus  the  SO4  anion 
of  Xa;S(J^,  in  virtue  of  charges  of  negative  electricity  which  it 
carrier  ill  very  readily  i)reeipitate  such  a  colloid  as  eolloidal 
iron  (lerrum  dialysatum,  V.  S.  P.),  which  is  charged  with  posi- 
tive electricity;  or  again,  this  colloid  itself  will  readily  preci|»itate 
arsenious  sulphide,  another  colloid  carrying  a  negative  charge. 
The  physiological  importance  of  the.se  reactions  lies  in  th<'  fact 
that  they  probably  explain  many  of  the  peculiarities  of  behavior 
of  mixture«  of  different  animal  fluid.s.  such  as  toxins  and  anti- 
toxins (see  p.  149). 

A  property  of  colloids  winch  is  closely  related  to  the  above  is 
that  of  adsurpfion.    This  means  the  tendency  for  dis.solved  sub- 


M 


l'IIYsIOl,<K}Y    FOR    I>K\'r.\I<    STrPF.NT!*. 


HtuiiCPN  to  Im'coiih'  pomlt'imcd  or  coiiceiit rated  at  the  surlacc  of 
colloidHl  inoli-ciilcH.  An  fXHinph*  '\n  the  wt'U  known  action  of 
chan-oal  wlu-n  Nhakt-n  with  colorftl  solutions,  [t  nMiiovcs  the  piif- 
inent  by  adsorbinK  it.  Atlsorption  is  duo  to  xurfarr  ti  imion, 
which  is  the  tciiHioii  croatt'd  at  th»>  surface  In'twccn  a  solid  and  a 
liijuid,  or  Iwtwccn  a  li(|uid  and  a  gas.  It  is  in  virtue  of  siirfacc 
tension  that  a  raindrop  assumes  more  or  less  spherical  shape. 
Since  colloids  exist  as  particles,  there  must  be  an  enormous  num- 
ber of  surfaces  throughout  the  solution,  tl'a,  is.  an  lMiohi  .>."<  sur- 
face tension.  Now  many  substances,  when  in  solution,  have  the 
power  of  decreasing  the  surface  tension,  and  in  doing  so  it  has 
been  found  that  they  accumulate  at  the  surface,  that  is  to  say, 
in  a  colloidal  solution,  at  the  surface  of  the  eolloidal  molecules. 
The  practical  application  of  this  is  that  it  helps  to  explain  the 
p'  vsical  ci.cmistry  of  the  cell,  the  protoplasm  of  which  is  a  eol- 
loi.i  j)  solution  containing  among  other  things  proteins  and 
liptflds.  The  latter  depress  the  surface  tension  and  therefore 
collect  on  the  surface  of  the  cell  and  form  its  supposed  mem- 
brane, whilst  the  proteins  exist  in  colloidal  .solution  inside.  It  is 
possibly  by  their  solvent  action  on  lipoids  that  ether  and  chloro- 
form 80  disturb  the  condition  of  the  rerve  cells  as  to  cause  anes- 
thesia. 

General  Nature  of  Enzymes  or  Ferments. 

To  decompose  proteins,  fats  or  carbohydrates  into  siinjile  mole- 
cules in  the  laboratory  necessitates  the  use  of  powerful  chemical 
or  physico-chemical  agencies.  Thus,  to  decompose  the  protein 
molecule  into  amino  bodies  retiuires  strong  mineral  acid  and  a 
high  temperature.  In  the  animal  body  similar  processes  occur 
readily  at  a  comi>aratively  low  temi)erature  and  without  the  use 
of  strong  chemicals  in  the  ordinary  sense.  The  agencies  which 
bring  this  about  are  the  enzymes  or  ferments.  These  are  all  col- 
loidal substances  (see  p.  ;}2).  so  that  they  are  readily  destroyed 
by  heat  and  are  precipitated  by  the  same  reagents  as  proteins. 
They  are  capable  of  acting  in  extremely  small  quantities.  Thus, 
a  few  drops  of  saliva  can  convert  large  quantities  of  starch  solu- 
tion into  sugar.    During  their  action,  the  enzymes  do  not  them- 


l     \ 


ENZYMK8. 


35 


srlvi'H  iiikIitko  jiiiv  pfmiaiH'iit  cliaiiKt'.  for  <'Vfii  afti-r  tln-y  have 
IwfH  actiiiK  for  a  lonn  time,  tlioy  fan  still  k<»  <»"  <l<>i"K  thoir  work 
if  fn'Hli  Tiiati'i-ial  Im-  Hiip|)lit'<l  upon  wliidi  to  act.  These  proper- 
ties are  explained  h.v  the  fact  that  they  act  coliih/liiiillij,  just  as 
the  oxides  of  iiitrojfeii  do  in  the  niannfaeture  of  sulphuric  aeid. 
That  is  to  say,  they  do  not  really  contribute  anythiuR  to  a  chemi- 
cal reaction,  hut  merely  serve  as  accelerators  of  reactions,  which 
however  wouhl  cM-eur.  though  vj-ry  slowly,  in  their  ab»«nice.  Thus, 
to  take  our  example  of  starch  aK«iii.  if  this  were  left  for  several 
years  in  tiie  prcsmcr  of  water,  it  would  take  up  some  of  the  water 
and  split  into  several  molecules  of  sujfar  (p.  :{4).  The  enzyme 
ptyalin  in  saliva  merely  acts  by  hurrying  up  or  accelerating  the 
reaction  so  that  it  oi'curs  in  a  few  minutes. 

Enzymes  differ  from  inorganic  eatalysers  in  the  remarkable 
sprcificity  of  thrir  ailion.  there  Iwing  a  special  enzyme  for  prac- 
tically every  chemical  change  that  oi-curs  in  the  animal  hotly. 
Thus,  if  we  act  on  any  of  the  sugars  calkul  disaccharides  (cane 
sugar,  lactose  and  maIto.se)  with  an  inorganic  catylytic  agent, 
such  as  hydrochloric  acid,  they  will  split  up  into  their  constitu- 
ent nmnosaccharide  molecule.-  whereas  in  the  bo<ly,  each  disac- 
charide  re(|uires  a  special  or  specific  enzyme  for  it.self.  The  en- 
zyme acting  on  one  of  them,  in  other  words,  will  be  absolutely 
inert  towards  the  others.  This  specificity  of  action  is  explained 
by  supposing  that  each  substance  to  be  acted  on  (called  the  sub- 
strat)  is  like  a  lock  to  open  which  the  proi)er  key  (the  enzyme) 
must  be  fitted. 

Enzymes  are  picitlutrlij  soisitive  towards  the  chemical  condi- 
tion of  the  fluid  in  which  they  are  acting,  more  particularly  its 
reaction.  Thus  the  enzyme  of  saliva  acts  best  in  neutral  reaction, 
whereas  the  enzyme  of  gastric  juice  acts  only  in  the  presence  of 
acid,  and  those  of  pancreatic  juice  in  the  presence  of  alkali. 
Enzymes  may  unfold  this  action  either  inside  or  outside  of  the 
cells  which  produce  them.  Thus,  the  enzymes  produced  in  the 
digestive  tract  act  outside  the  gland  cells,  but  the  enzyme  of  the 
yeast  cell  acts  in  the  cell  itself  and  is  never  secreted.  The  former 
are  esilled  ( xirnrilluhir  enzymes  and  the  latter  intracellular.  The 
activities  of  intracellular  enzymes  are  much  more  liable  to  be 


36 


I'IIYsI()I,(H;V    FdU    DKNTAI.    STfDF.XTS. 


iiitfrfcrcd  witli  hy  iiiifiivoi-Hhlc  coiiditioiis  tliaii  tlioso  of  oxtra- 
cfllular  cii/yint's.  This  is  hecaust'  tlit-  fornicr  Ix'eonic  inaetive 
whciK'vor  aiiythiii},'  ((ccurs  to  destroy  tlit-  |)rotoi)Iasin  of  the  ocH 
ill  wliicli  thf'y  act.  Tin-  living  j)n>to|>lasin  is  incfssary  to  bring 
the  suhstrat  in  contact  witii  thcni.  On  this  aico\n)t  enzymes  used 
to  he  dassitietl  into  orf/uiiUi  d  and  nii(>r<i<tiiii<  d.  We  know  that 
there  really  is  no  difference  in  the  en/yine  itself:  the  only  ditfer- 
eiice  is  with  rejfard  to  the  i)lace  of  activity.  The  cells  that  coni- 
l)ose  the  tissues  of  animals  perform  their  various  chemical  activi- 
ties in  virtue  of  the  intracellular  enzymes  which  they  contain. 
These  are,  therefore,  tlie  chemical  reagents  of  the  laboratory  of 
life.  After  the  animal  dies,  the  intraceliulai'  enzymes  may  go 
on  acting  for  a  time  and  digest  the  cells  from  within.  This  is 
called  (iiitoljjsis. 

Enzymes  are  classifiitJ  info  (/roups  according  to  the  nature  of 
the  chemical  action  which  they  accelerate.    Thus: 

Hydrolytic  enzymes — cause  large  molecules  to  take  up  water 
and  s])lit  int(»  small  molecules.  (.Most  of  the  digestive 
enzymes  belong  to  this  class.) 

Oxidative  enzymes  (oxydases) — encourage  oxidation. 

Deamidating — remove  NIT,  gnrnj*. 

Coagulative — coiiveit  solul)le  into  insoluble  proteins. 

Each  group  is  further  subdivided  according  to  the  nature  of 
the  substrat  on  which  the  enzymes  act ;  e.  g..  hydrolytic  enzymes 
are  subdivided  into  amylolases — acting  on  starch;  invertases — 
acting  on  disaceh-irides;  jtroteases — acting  on  i)roteins;  ureases 
— acting  on  urea,  etc. 

When  enzymes  are  re])eatedly  injected  into  the  blood,  or  under 
certain  other  conditions,  they  liave  the  i)ower,  like  toxines.  of 
|)ro('ucing  nntiriuymrs.  As  their  name  signifies,  these  are  bodies 
whi-  h  retard  the  action  of  enzymes.  Thus,  if  some  blood  serum 
from  ail  animal  into  which  trypsin  has  been  injected  for  soTue 
days  previously  be  mixed  with  a  trypsin  solution,  the  mixture 
will  digest  protein  very  slowly,  if  at  all,  when  compannl  with  a 
mixture  of  the  same  amount  of  trvpsin  and  protein  (see  also 
p.  78). 


CHAPTER  111. 

DIGESTION. 

Necessity  and  General  Nature  of  Digestion:   Digestion  in  the 

Mouth. 

Tln'  iii'vcr-ecasiiifr  process  of  coinbiistioii  tliat  fiocs  on  in  tlit^ 
animal  body,  as  well  as  the  con.stant  wear  and  tear  of  tlu'  tissues, 
makes  it  necessary  that  tiie  supply  of  fuel  and  of  buildinj;  mate- 
rial be  fre(|Uently  renewed.  For  this  purpose  food  is  taken.  This 
food  is  eomi)o.sed  of  fats  and  earbohytlrates.  whicii  are  mainly 
fuel  materials,  of  inorfjanie  salts  and  water,  wiiieh  are  neees- 
sai'y  to  repair  tiie  worn  tissues  and  (»f  proteins  whieii  are  botli 
fuel  and  repair  materials,  and  are  tiierefore  tiie  most  important 
of  the  organic  f ood.st utt's.  Tiie  blood  transports  tiie  fwKlstutTs 
from  tile  dijjestive  canal  to  the  tissues.  In  the  digestive  canal  tlie 
foodstuffs  are  digested  iiy  hydrolyzing  enzymes  (see  j).  :{6), 
which  are  furnislied  partly  in  the  secretions  of  the  digestive 
glands  and  partly  from  the  numerous  micro-organisms  that 
swarm  in  the  intestinal  contents.  The  enzymes,  as  we  have  seen, 
are  very  discriminative  in  their  action,  for  not  only  is  the  enzyme 
for  protein  without  action  on  a  fat  or  carbohydrate,  but  each  of 
the  different  stages  in  i)rotein  break-down  i'e(|uires  its  own  pe- 
culiar enzyme.  It  becomes  necessary  therefore  that  tlu'  enzymes 
be  mi.\ed  with  the  food  in  projier  sei|Ueiice.  and  to  render  this 
po.ssible  the  digestive  canal  is  found  to  be  divided  into  special 
compartments,  such  as  the  mouth,  the  stomach,  the  small  intes- 
tines, etc.,  each  i)rovided  with  its  own  a.ssortnieiit  of  enzymes 
and  with  some  mechanism  by  whicli  it  can  ))ass  on  the  food  to 
the  next  stage  when  it  has  been  sntlieiently  digested. 

Such  correlation  between  the  different  stages  of  digestion 
necessitates  the  existence,  in  the  different  levels  of  the  ga.stro- 
intestinal  tract,  of  nieehanisms  which  are  specially  develojied  to 


38 


PHYSIOLOGY   FOR   DENTAL   STUDENTS. 


t 
H 

I 


briiij?  about  the  right  secretion  at  the  right  time.  These  lueeli- 
anisnis  are  of  two  es.sentially  different  types,  a  luri-oiis  reflex 
control,  and  a  chemical  or  ''hormone"  control.  The  nervous  con- 
trol i.s  exercised  througii  a  nerve  center  which  is  eaUed  into  activ- 
ity by  afferent  stimuli  whidi  proceed  from  sensory  nerve  endings 
or  receptors  (see  p.  244)  that  are  especially  sensitized  so  as  to 
be  stimulated  by  some  projurty  of  food  (its  taste  or  smell,  or 
some  local  action  on  the  nerve  endings).  Tliis  type  of  control 
exists  where  prompt  respoi.M'  of  the  glandular  secretion  is  impor- 
tant, as  in  the  mouth  and  in  the  early  stages  of  digestion  in  the 
stomach.  The  hormone  control  consists  in  the  action  directly  on 
the  gland  cells  of  substances  which  have  been  absorbed  into  the 
blood  from  the  mucous  membrane  of  the  ga.stro-intestinal  tract. 
The  production  of  these  substances  depends  upon  the  nature  of 
the  contents  of  the  digestive  tube.  This  is  a  more  sluggish  jiroe- 
ess  of  control  than  tlx-  lu'rvous,  but  it  is  all  sutiRcient  for  the  cor- 
relation of  most  of  the  disgestive  functions. 

These  considerations  point  the  way  to  the  scheme  which  we 
nuist  adopt  in  studying  the  process  of  digestion  ;  we  must  explain 
how  each  digestive  juice  comes  to  be  secreted,  what  action  it  has 
on  the  foodstuffs,  and  what  it  is,  after  each  stage  in  digestion  is 
completed,  that  controls  the  movement  onward  of  the  food  to 
the  next  stage.  And  when  we  have  followed  each  fmnlstuff  to 
its  last  stage  in  digestion,  we  may  then  procee  '  to  study  the 
means  by  which  the  digested  foodstuffs  are  absorbed  into  the  cir- 
culating fluids,  and  in  wliat  form  they  ai'e  carried  to  the  tissues. 

On  account  of  the  varying  nature  of  their  focxl  we  find  that 
the  digestive  system  differs  considerably  in  different  groups  of 
animals.  In  the  omnivora,  such  as  man,  the  digestive  canal  be 
gins  with  the  mouth  cavity,  in  which  the  fcMul  is  broken  up  me 
chanically  and  is  mi.ved  with  the  .saliva  in  suflHcient  amount  to 
render  it  capable  of  being  swallowed.  The  .saliva,  by  containing 
starch-splitting  ferment,  also  initiates  the  digestive  process.  The 
food  is  then  carried  by  way  of  the  (esoi)hagus  to  the  stomach,  in 
the  near  or  cardiac  end  of  which  it  collects  and  becomes 
gradually  pei-meated  by  the  acid  gastric  juice.  It  is  then  cauglit 
up,  portion   by    portion,    by    the    peristaltic    waves    of    the 


SAMVAKY    ?KCKET1()N. 


39 


further  or  pyloric  end  of  the  stomach  and  after  Ix-ing  thor- 
oughly broken  down  by  this  movement  and  partially  digested 
by  the  pepsin  of  gastric  .juice,  is  passed  on  in  portions  into 
the  duodenum,  where  it  meets  with  the  secretions  of  the  pancreas 
and  liver.  These  secretions,  acting  along  with  auxiliary  .iuices 
secreted  by  the  intestine  itself,  ultimately  bring  most  of  it  into  a 
state  suitable  for  absorption.  What  the  digestive  juices  leave 
unacted  on  bacteria  attack,  especially  in  the  ca'cum,  so  that  by 
tiie  time  the  fo'^'l  has  gained  the  large  intestine  it  has  been  di- 
gested as  fai  'Hu  be.  In  its  fui-ther  slow  movement  along 
the  large  int  ne  process  of  absorption  of  water  proceeds 
rapidly. 

Disturbances  in  the  digestive  process  may  be  due  not  only  to 
l)ossible  ina(le(iuacy  in  the  secretion  of  one  or  other  of  the  diges- 
tive juices,  but  also  to  disturbances  in  the  movements  of  the 
digestive  canal.  Such  disturbances  will  not  only  prevent  the 
forward  movement  of  the  food  at  the  proper  time,  but,  by  failing 
to  agitate  the  food,  they  will  prevent  its  proper  admixture  with 
the  digestive  juices,  for  of  course  an  enzyme  acts  more  i-apidly 
when  the  mixture  is  kei)t  thorotighly  agitated  with  the  food  than 
when  it  is  stagnant. 

Digestion  in  the  Mouth. 

Salivary  Secretion. — In  the  mouth,  besides  its  preparation 
for  swallowing,  by  mastication,  etc.,  the  food,  maiidy  on  accmint 
of  its  taste  and  smell,  stimulates  sensory  nerve  endings  which, 
by  acting  on  nerve  centres,  set  agoing  .several  of  the  digestive 
secretions.  The  first  of  these  is  the  .secretion  of  the  salivary 
glands.  On  account  "f  their  ready  accessibility  to  experimental 
investigation,  very  extended  studies  have  been  made  of  the  sali- 
vary glands,  and  from  tiiese  studies  some  of  the  most  important 
physiological  truths,  concerning  the  luiture  of  the  nervous  con- 
trol of  glands  in  general,  have  been  drawn.  Of  the  tliree  salivary 
glands  in  man.  the  parotid  secretes  a  watery  saliva  usually  con- 
taining the  enzyme,  ptyalin,  ami  the  submaxillary  and  subling- 
ual secrete  a  sticky  saliva  containing  mucin,  usually  along  with 
some  ptyali'i.    When  the  glands  are  not  secreting,  the  cells  that 


I 


40 


I'llYSIOLOUV    FUR    DENTAL   STl  DENT.^. 


(«oiiii)ost'  thcni  arc  cngagt'd  in  propariiiji  material  to  bo  spcrotcd. 
liy  microscopical  examination,  this  material  is  seen  in  tlio  proio- 
i)lasm  of  the  cells  (Fijr.  2)  as  granules,  which  are  extremely 
small  in  the  scrons  jrland  cells,  but  much  larjrer  in  the  mucous. 
In  both  tyi)es  (tf  frbnKl  tiie  fyranulcs  so  crowd  the  cell  that  the 
nucleus  becomes  indistinct  and  the  cell  itself  much  swollen. 
After  the  gland  has  been  active,  the  granules  disappear,  being 
evidently  discharged  from  the  cell  into  the  duct  of  the  gland. 
The  granules  are  believed  to  rei»resent  the  precursors  of  the 
ptyalin  or  mucin  of  saliva — hence  their  name  of  "zynu)gen"  or 
"mother  of  ferment"  granules— rather  than   these   substances 


Kij,'.  -'. — (Vlls  of  iKii'otid  Blaiul  .'showing  z.vmoBeii  Kiaiiulfs  :  .1.  after  piii- 
loiiHcd  rest;  B,  after  a  nioileiate  stcivtiDii ;  C.  after  proloiiHcl  .stHrctinii. 
(  (..aiitfU'.v. ) 


themselves.  Watery  or  .saline  extracts  of  tlie  glands  contain 
neither  mucin  nor  ptyalin.  nor  does  the  addition  of  actic  acid  to 
a  nnicons  gland  cause  any  precipitate  of  mucin :  indeed,  it  has 
an  entirely  opposite  action,  it  cau.ses  the  granules  to  swell. 

The  Nerve  Supply  of  the  Salivary  Glands.— The  nerve  Hbcrs 
sujiplying  the  glands  are  of  the  autonomic  or  visceral  type  (see 
p.  277),  and  they  include  sympathetic  and  cerebrospinal  fibers. 
The  sympathetic  fibers  are  derived  fnmi  cells  in  the  lateral  horns 
of  the  .spinal  cord,  from  which  they  emerge  by  the  upper  thi-ee 
or  four  thoracic  roots,  and  after  ascending  as  niedullate<l  fibers 
in  the  cervical  sympathetic,  terminate  as  synapses  around  the 
cells  of  the  superior  cervical  ganglion.  The  axons  of  these  cells 
proceed  as  non-medullated  post-ganglionic  fibers  along  the  near- 
est  Nfssels  to  tlie  respective    glanils.     The    cerebral    autonomic 


^AI.IVAUV     SKCUKTION. 


41 


Hlu-rs  arise  from  a  cfiitt-r  in  the  mcilulla  and  i)ro<MM'(l  to  tlu' 
jrlands  l>y  variouis  routi-s:  those  to  the  submaxillary  and  suit- 
lingual  glands  in  the  chorda  tympani.  and  those  to  the  jtartoid 
l)y  way  of  the  tympanic  branch  of  the  <;losso-pliaryngeal.  The 
ganglion  cells  connected  with  tl.e  cerebral  fibers  are  situated 
more  or  less  jteripherally ;  in  the  case  of  the  subnuixillary 
they  are  embedded  in  the  substance  of  the  gland;  in  the  case  of 
the  sublingual  gland,  in  the  connective  tissue  of  the  so-called 
submaxillary  triangle,  and  in  the  case  of  the  jtarotid,  in  the  otic 
ganglion  (Fig.  ;i). 

In  both  cerebral  and  sympathetic  nerves  there  are  two  vari- 
eties of  fibers,  the  one  nisotnotur,  the  other  s<  cnforii.     The  for- 


Kij;.    ;{, The   in-ivi-   siipiily   of   tln'    sul'iiiiixilhiiy    kI;iiii1  :    l.i.   !iii«unl   iici\e: 

r.    t.,  chorda    t>  inpaiii  :    ;/.    Kb'iid       Whaiton'.s   duct    is    liKatcd    and    it   wiU    In- 
'noticed  that   the  chorda   leaves   tile   linKUal   nerve.   Just   Itefore   tills  criiss.s  the 
duct,    thus   foinniig  the  .subniaxillaiv    liianKle,      ((Maude    Bernard.) 


mer.  in  the  cas.'  of  the  cerebral  nerves,  are  dilator  in  their  action, 
but  in  the  sympathetic  they  are  constrictor.  On  account  of  the 
association  of  secretory  and  vasodilator  fibers,  in  the  cerebral 
nerves,  stinndation  leads  to  the  secretion  of  large  (|uantitie.s  of 
saliva,  the  amount  of  which,  as  well  as  its  percentage  of  organic 
and  inorganic  constituents,  varies  within  certain  limits,  with  the 
strength  of  the  stimulus.  Althougli  .secretory  activities  also  be- 
eomo  excited  when  the  sympatlietic  nerve  is   sfimulaled.    as    is 


42 


PMYSIOLiXJV    FOB    DKNTAL    STUDENTS. 


revealed  by  histolopioal  exainination  of  the  gland,  there  is  only 
a  slight  flow  of  saliva  from  the  duct  beeause  of  the  eonconiitant 
eurtailment  of  the  blood  supply.  In  so  far  as  actual  secretion  of 
saliva  is  concerned,  the  net  result  of  stimulation  of  either  nerve 
is  therefore  dependent  tlpon  whether  dilatation  or  constriction 
of  the  blood  vessels  of  the  gland  occurs,  and  this  might  lead  us 
to  conclude  that  the  secretion  is  secondarj'  to  changes  in  the 
blood  supply ;  in  other  words,  that  it  is  unnecessary  to  assume 
the  independent  existence  of  specific  secretory  nerve  impulses. 
That  such  secretory  fibers  do  exist,  however,  is  established  by 
many  facts.  Two  of  these  are:  (1)  The  vessels  still  dilate  but 
no  secretion  o<'Curs  after  a  certain  amount  of  atropin  has  been 
allowe'd  to  act  on  the  gland.  This  alkaloid  paralyzes  the  secre- 
tory nerve  fibers,  but  has  no  action  on  those  concerned  in  vaso- 
dilation. (2)  If  the  secretions  were  merely  the  result  ot  in- 
creased blooil  sui)ply,  in  other  words,  were  a  filtrate  from  the 
blood,  the  pressure  in  the  duct  would  at  all  times  be  less  than 
that  in  the  blootl  ve.s.sels,  but  this  is  not  the  case,  for  dui-ing  stim- 
ulation of  the  cerebral  nerves  the  duct  pressure  may  rise  far 
above  that  of  the  blood  vessels. 

But  it  must  never  be  lo.st  sight  of  that  although  both  kinds  of 
fibers  do  exist,  thry  are  very  closely  associated  in  their  action. 

The  Reflex  Nervous  Control  of  Salivary  Secretion.— The 
structural  differences  between  the  parotid  and  submaxillary 
glands  suggest  that  their  functions  may  not  be  the  same;  that 
their  respective  secretions  nuist  be  rei|uired  for  different  pur- 
poses. To  put  this  suppf)sition  to  the  test,  it  becomes  Jiec«'.ssary 
to  adopt  some  means  by  which  the  conditions  calling  forth 
the  secretion  of  each  gland  may  be  .separately  studied.  This  can 
be  accomplished  by  a  small  surgical  operation  in  which  the  ducts 
are  transplanted  so  as  to  discharge  tlirough  fistula;  in  the  cheek, 
the  secretion  being  easily  collected,  by  allowing  it  to  flow  into  a 
funnel  which  is  tied  in  place. 

In  general, two  distinct  types  of  stimuli  may  call  forth  secretion 
of  one  or  other  gland,  immely:  (1)  dinct  sfimulnlion  of  semory 
nerve  endings  in  the  mouth,  and  (2)  psifiholoyual  stimuli  in- 
volving more  or  less  of  an  association  of  ideas. 


SALIVARY    SECUfcTION. 


43 


Of  the  stinmli  which  eauso  socretion  by  acting  on  sensory  nerve 
endings  in  the  moutli.  some  influence  the  parotid,  others  the  sub- 
maxillary gland,  and  different  stimuli  produce  different  effects. 
Even  for  pure  mechanical  stimulation  of  the  buccal  mucosa,  u 
marked  degree  of  discrimination  is  shown;  thus,  sihooth  clean 
I)ebbles  may  be  rolled  around  in  the  mouth  and  yet  cause  no 
.saliva  to  be  secreted,  whereas  dry  sand  will  immediately  cause 
the  parotid  to  discharge  enormous  (luantities    of    thin    watery 
juice.    Similarly  dry  bread  crumbs  invoke  copious  parotid  secre- 
tion, bread  itself  having  little  effect;  water,  ice,  etc.,  are  ine- 
but  if  they  contain  a  trace  of  acid  an  abundant  secretion  is  i 
stantly  poured  out.     It  is  plain  in  all  these  cases  that  the  pui- 
l)ose  of  the  secretion  is  to  assist  in  the  removal  or  neutralization 
of   the    substance   which    is   present   in  the  mouth.     The  thick 
mucous  secretion  of  the  submaxillary    and    sublingual    glands 
seems  to  depend  more  on  the  chemical  nature  of  the  food  than  on 
its  mechanical  state,  boiled  potato«'S,  hard  boiled  eggs,  meat,  etc.. 
causing  the  secretion  of  a  thick  slimy  saliva,  which  by  coating 
the  food  a.ssists  swallowing.    The  relish  for  the  food  seems  to  be 
of  little  account  in  influencing  the  secretion  of  sidiva,  for  noxious 
substances,  or  those  that  arc  acid,  or  very  salty,  call  forth  much 
more  secretion  than  do  savory  morsels.    Although  mere  mechani- 
cal stimulation  is  not  in  it.self  an  ade(|uate  stinuilus,  yet  move- 
ment of  the  lower  jaw  is  (piite  effective,  as  for  example  in  chew- 
ing, or  when  the  mouth  is  kept  open,  as  by  a  gag  in  a  dental 
oi)eration. 

The  stimulus  does  not,  however.  re<(uire  to  be  applied  to  the 
biN'cal  mucosa  itself;  it  may  be  /w.i/c/i »•  or  associationnl.  and 
here  again  a  remarkable  (iiscrimiiiation  is  evident,  althougli  the 
response  is  not  so  predictable  as  when  the  stimulus  is  local. 
Thus,  when  dry  bread  or  sand  is  sliown  to  a  dog  to  whom  previ- 
ously these  substances  have  been  given  by  mouth,  salivation  fol- 
lows, but  this  is  not  the  case  when  moist  bread  or  pebbles  are 
offered.  Appetite  plays  an  in>-)ortant  part  in  this  psychic  reflex, 
for  when  dry  food  is  shown  to  a  fasting  animal,  salivation  is 
marked,  but  may  cause  no  secretion  when  it  is  offered  to  a  well- 
fed  animal.    It  is  possible  in  this  case,  however,  that  there  may 


\ 


44 


PiiY!?10L0GY    FOB   UENTAI.   STUDENTS. 


J 


be  inhibition  of  the  Kbuulular  activities  on  iiceount  of  tlie  j)n's- 
cnce  of  foot!  proiliu-ts  in  the  blood.  Porhaps  tlu'  most  intt'ivsting 
fact  of  all  i.s  that  even  a  fa.stinp  animal  will  after  a  time  fail  to 
.salivate  if  lie  be  repeatt-dly  shown  fomi  which  causes  a  secretion, 
but  which  he  is  not  permitted  to  ffet.  The  resjionse  is  immedi- 
ately established  again,  however,  if  some  food,  or  indeed  some 
other  object,  be  placed  in  the  mouth.  A  hungry  animal  will  even 
.salivate  when  he  hears  some  sound  which  by  previous  experience 
he  has  learned  to  a.ssociate  with  feeding  time.  The  psychic 
reflexes  are  evidently  dependent  u[)on  an  asswiation  of  ideas  (a 
nervous  integration,  see  p.  242)  ;  they  are  conditioned  reflexes, 
and  are  therefore  the  residt  of  a  certain  degree  of  education. 
They  are  easily  rendered  ineffective  by  confusing  the  u.sual  as.so- 
ciations. 

General  Functions  of  Saliva.— Th.-se  observations  indicate 
that  a  very  important  function  of  the  saliva  is  what  we  may  call 
a  mrchnniail  one.  namely,  either  to  flood  the  mouth  cavity  with 
Muid  and  so  to  wash  away  objectionable  objects  in  it,  or  to  lubri- 
cate the  food  with  mucin  and  .so  facilitate  .swallowing.    The  sol- 
vent action  of  saliva  is  also  important  for  the  act  of  tasting  (see 
p.  2!»5).    Its  chnniail  activities  in  many  animals  seem  to  be  lim- 
ited to  the  neutralizing  })roperties  of  the  alkali  which  is  present 
in  it,  but  in  man  and  the  herbivora  it  also  contains  a  certain 
amount  of  a  diasiatic  enzyme,  ptyalin.  which  can  ((uickly  con- 
vert cooked  starches  into  dextrines  and  maltose.    Even  when  this 
action  is  most  pronounced,  however— for  it  varies  consitlerably 
in  different  individuals — it  cannot  proceed  to  any  extent  in  the 
mouth  cavity,  partly  on  account  of  the  .short  time  food  renuiins 
here,  and  partly  becau.se  many  starches,  as  in  biscuits,  are  taken 
more  or  less  in  a  raw  state.     In  some  animals,  such  as  the  dog. 
the  .saliva  has  no  diastatic  action  whatever.    Although  there  can 
therefore  be  little  diastatic  digestion  in  the  mouth,  a  good  deal 
may  go  on  in  the  stomach,  for  the  saliva  that  is  swallowed  along 
with  the  foo<l  does  not  become  destroyed  by  the  gastric  juice 
until  some  thirty  minutes  after  the  food  has  gained  the  stomach. 
Although  mastication  of  the  food    and    its    preparation    for 
swallowing  are  undoubtedly  the  nuiin  functions  of  the  mouth  cav- 


>ii 


;.\MV.\RY    SKCKKTIDX. 


45 


ity.  aiiotluT  exists  wbicli  is  of  v<'ry  Krcat  iinportiiiict'  for  proper 
(liKestion;  this  is  the  stimuhition  of  the  taste  nerve  eiuliii>;s. 
and,  for  foo<ls  with  a  flavor,  of  those  of  the  oifaetory  nerve  in  tlie 
posterior  nares.  Sueli  stimulation  not  only  gratifies  the  appetite, 
hut  it  serves  as  the  a(ie(|uate  stiiiiuliis  to  set  HKoin>j  the  st-eretion 
of  the  Kastrie  juiee.  Without  any  relish  for  food,  digestion  as 
a  whole  materially  suffers,  and  for  this  reason  unpalataltle  food 
is  always  more  or  less  indigestihle. 


'1 


CHAPTER  IV. 

DICJKSTIOX  (Cont'd). 

The  0heini5tr7  of  Saliva  and  the  Relationship  of  Saliva  to 

Dental  Caries. 

A  knowlfxlge  of  tlip  composition  and  chomical  proportios  of 
saliva  is  of  ^reat  iniportancp  because  of  the  undoubted  etiologi- 
cal relationship  wliieh  exists  between  this  secretion  and  dental 
caries.  Mixed  saliva  wlien  freshly  secreted  is  a  watery,  more  or 
less  opalescent  and  sticky  fluid,  often  containing  small  masses 
of  mucin,  but  on  standing  it  becomes  cloudy  because  of  precipi- 
tation of  calcium  carbonate.  Its  specific  gravity  is  1002-1006, 
and  it  contains  about  0.05  per  cent  of  solids.  The  saliva  from 
the  sublingual  and  submaxillary  glands  is  very  much  richer  in 
solids  than  that  from  the  parotid.  The  parotid  saliva  also  differs 
from  that  of  the  other  glands  in  containing  no  mucin,  although 
it  is  often  rich  in  ferment.  Th(!  solid  constituents,  with  some  of 
their  properties,  are  as  follows: 

'  (ilycoprotein  (mucin)  :  precipitated  by  acid. 
Other  proteins:  coagulated  by  heat. 
Organic.  .  .■{  Ptyalin  :  a  starch-splitting  enzyme. 

Potassium  sulphocyanide :  gives  ji  red  color  witli 
ferric  chloride. 


Sodium  chloride: 
Potassium  chloride : 
Calcium  bicarbonate 
Calciinn   carbonate : 
Inorganic,  ^l       standing. 

Calcium  and  magnesium 

phosphates : 
So<lium   and    potassium 

phosphates : 

Organic   Constituents. — Mucin    is    the    substajtco    to    which 
saliva  owes  its  stickiness.    Being  a  glycoprotein,  it  yields  reduc- 

46 


give  a  precipitate  with  sil- 
ver nitrate, 
in  fresh  saliva, 
precipitated    in   saliva    after 


Have  an  important  re- 
lationship to  the  neu- 
tralizing properties 
of  saliva. 


CHEMISTRY    HV    SALIVA. 


47 


iiiK  supnr  when  it  is  liytlrolyzcd.  as  by  boiliiifr  with  acid.  It  was 
at  one  tiiin'  siiKucsttMl  that  siif^ar  miuht  sniin-tini»>H  appi'ur  in  the 
saliva,  as  a  n-siilt  of  ])aotcrial  action  in  the  inoutii,  and  bo  rcspon- 
sibh-  for  caries  of  the  teeth.  Tlie  anionnt  is,  liowevcr,  so  very 
.small  in  comparison  with  the  iiiKcsti-d  carboliydrates  that  it  can 
be  entirely  disre^anUHl. 

phiolin. — This  belonjfs  to  tlie  class  of  diastatic  or  am.vlolytic 
enzymes,  convertinK  starch  into  siinar.  It  is  not  so  powerful  as 
tile  similar  enzyme  in  pancreatic  .jnice  (.see  p.  74),  for  it  has 
no  action  on  uncooketl  starch,  which  the  latter  has.  It  acts  best 
in  neutral  reaction  and  in  the  presence  of  .siMlium  chloride,  but 
is  little  atTected  by  a  small  dcj^ree  of  akalinity.  On  the  other 
hand,  it  is  readily  destroyed  by  acids  and  by  higher  deRrees  of 
alkalinity.  These  facts  are  of  importance  in  connection  with  the 
continuance  of  action  of  .saliva  after  it  has  Im-cii  swallowed,  for 
although  the  food  remains  in  the  mouth  for  nuich  too  brief  a 
period  to  permit  of  more  than  a  trace  of  sugar  iK'ing  formed 
here,  yet,  after  the  stomach  is  reached,  i)t.valin  may  continue  to 
act  for  about  half  an  hour.  The  ptyalin  content,  however,  varies 
very  considerably  in  different  individuals. 

Ptyalin  convi-rts  starch  into  the  sugar  maltose,  so  called  be- 
cause it  is  also  formed  by  the  action  of  the  diastase  of  nudt.  As 
intermediate  substances  are  formed  the  ilextrins.  two  of  which 
are  distinguishable  on  account  of  their  l«>havior  towards  iodine ; 
the  first  dextrin,  called  erythrodextrin,  gives  a  brown  color,  while 
the  next  gives  no  color  and  is  called  achrcH)dextrin. 

It  has  been  suggested  that  a  deficiency  of  ptyalin  may  pre- 
dispose to  caries  of  the  teeth  becauw.  under  such  circumstances, 
a  large  amount  of  dextrin  is  formed,  which  being  very  sticky  in 
character  adheres  to  the  teeth  and  becomes  u  suitable  nidus  for 
l)acterial  growth. 

Potassium  Stdphocyanidr  {sulphotiiinuili). — This  salt  has 
the  formula  KCNS,  and  is  usually  present  in  human  saliva 
to  the  extent  of  about  0.01  per  cent.  It  is  produced  in  the  bloo<l 
whenever  cyanides  or  organic  nitrites  make  their  a  nearance  in 
the  organism,  one  source  for  these  being  possibly  p  icin  nieta 
bolism  (p.  108).    It  is  excreted  from  the  blood  into  the  urine  as 


48 


PliyslOI,<»OY    Kim   I>KNT\I,   STIDKSTS. 


Well  as  the  sjiliva.     In  contrast  to  cyanidt's  it  is  non-poisonnuH.  ho 
Y\  that  it  r(']in'>M'nts  the  inociioiis  form  into  vvliicli  tln-sc  milwtanciM 

/  ari'  convt'rtfil. 

The  cht-niiral  tt-st  uscil  for  its  detect  ion  is  tlie  red  color  which 
it  Kives  with  a  solution  of  ferric  i-hlori«le  (FeCI,).  Soinetiines, 
however,  the  reaction  is  not  very  detinite,  in  whieli  case  the 
method  of  Uuntinj;  shoidd  he  employed.  ThiN  is  pcrforme«l  ns 
follows:  Slowly  evaporate  5  c.  c.  of  saliva  in  a  watch  {rlass  and 
while  stirring  with  a  kI«ss  rod  ad<l  a  few  drops  of  a  2")  per  cent 
solution  of  KeCI,.  Pour  almut  "»  c.  c.  of  a  mixture  of  5  parts 
arnyl  alcohol  and  2  j)arts  ether  over  the  residin-.  and  after  stir- 
ring dwant  into  a  test  tul)e.     if  sulphocyanide  is  present,  the 

alcohok'tluT  will  I onie  red.     Heiizoat.    and  aceto  acetic  arid 

may  n'wv  a  similar  reaction,  but  most  of  the  other  substances 
whicdi  might  interfere  witii  tiic  test,  as  when  it  is  done  by  merely 
addinj;  FeCI.,  to  saliva,  are  eliminated  by  Hunting '.s  method. 

All  this  care  and  interest  in  the  testing  for  KCXS  ha.s  arisen 
becau.se  of  the  supposition  tliat  the  amount  of  this  substance  in 
saliva  might  have  soi.ie  relationship  to  caries  of  the  tectli.  It 
wa.s  suggested  that  it  might  confer  on  the  saliva  somewhat  of  an 
anti.septic  action  and  thus  destroy  the  bacteria  that  are  the  cause 
of  caries.  Careful  work  by  ISunting.  by  (}ies  and  others  has, 
however,  shown  that  this  hypothesis  is  untenable. 

Inorganic  Constituents. — Two  important  questions  arise  in 
ponnection  with  these,  viz:  (1)  their  relationshij)  to  the  reaction 
of  the  saliva;  (2)  the  conditions  which  control  the  precipitation 
of  calciunv  carbonate  and  ])hosphate  and  tlu'  dei)osition  of  the 
precipitate  on  the  teeth  in  the  form  of  tartar. 

The  Rk.\cti(i\  ok  thk  Sai,iv.\.— Tested  with  litmus  pa[)er  sa- 
liva is  more  or  less  alkaline  and  it  is  distinctly  .so  towards  lac- 
moid  and  Congo  red.  but  it  is  acid  when  tested  with  phenolph- 
thalein.  It  is  tlui.s  said  to  1,  Miiiphoteric,  like  bloinl  and  urine 
Dilficulty  in  deciding  as  to  *iie  r  action  of  saliva  is  partly  due 
to  the  fact  that  it  changes  :)m  sending  becau.se  carbon-dioxide 
(('()„)  is  di.s.sipated,  thus  niaki:)g  it  more  alkaline.  To  succeed 
in  deterndning  the  reaction  of  saliva,  wt  must  therefore  under- 
stand to  what  its  amphoteric  behavior  is  due   and  we  must  con- 


fllKMIsTRY    (»K   SAI-IVA. 


49 


staiitly  Iwiir  in  iiiiiul  that  ihf  n-al  n-actioii  of  a  fluid  is  \\\v 
ratio  iH'twci'ii  "  ■<■  II-  ami  (Ul-ions  (set-  p.  :!()).  15y  aiialysiH 
saliva  liaH  hofu  louinl  to  contain  plioNphates  and  caHionatcs,  both 
of  which  arc  capabh-  of  cxistintf  cither  as  acid  or  alkaline  Halts, 
that  is  to  say.  as  NalKPO,  and  NallCO,,  (acid  salts)  or  Na.Hl'O, 
and  .\a.,(*(),,  (alkaline  sjiUsK  Since  the  reaction  Kiven  by  solu- 
tions which  contain  such  mixtures  of  acid  ami  alkulinc  salts 
depends,  first,  on  the  relative  proportioii.s  of  these  .salts  and, 
secondly,  on  the  exact  indicator  employed  to  test  the  reaction 
(see  p.  ;n).  it  is  plain  that  the  reaction  of  the  sidiva  as  ordi- 
narily tested  must  b*  very  haphazard. 

To  determine  the  H-ion  concentra  "i  '>.  saliva,  some  of  this 
fluid  is  diluted  about  ten  times  with  ..i.stilled  water,  which  has 
been  boiled  and  cooled  so  as  to  free  it  of  carbon  dioxide,  ami 
0.5  c.  c.  of  paranitrophenol  solution  is  added.  The  resulting  tint 
is  then  pomjiared  with  that  obtained  by  adding  0.")  c.  c.  of  the 
same  indicator  to  each  of  a  series  of  test  tubes  containing  vary- 
ing jn-oportions  of  acid  and  alkaline  pho.sphate  solutions  {^/,^ 
normal).  The  tint  of  this  series  which  matches  with  that  of  the 
.saliva  indicates  the  H-ion  concentration  of  the  latter  k-cause 
this  is  known  in  the  standard  from  the  proportion  of  the  two 
phosphates  present. 

TiiK  Method  ok  Mk-vsirlnc  the  Neutr-MJ/ixo  Power  of  Sa- 
i.iVA. — Interi'sting  thouKh  Il-ion  results  may  be,  they  do  not  aj)- 
pear  to  be  of  any  practical  value  in  connection  with  the  relation- 
ship between  the  saliva  and  caries  of  the  teeth.  To  study  this 
([uestion  it  has  been  found  to  l)e  of  more  value  to  determine  fhi 
IK  ntmlaing  power  of  saliva  ;  that  is,  to  find  out  how  much  stand- 
ard acid  or  alkali  we  nnist  add  to  a  measured  quantity  of  saliva 
in  order  to  get  a  chancre  with  one  or  more  of  the  above  indicators. 
In  doing  this,  however,  we  are  immediately  struck  with  the  fact 
that  the  reaction  does  not  change  in  ]>roporti()n  to  the  amount 
of  acid  or  alkali  added,  but  that  the  saliva  under  .such  conditions 
p()s.sc.sses  the  property  of  changing  very  slowly  in  reaction.  This 
same  property  also  exists  in  the  blooil,  and  it  depends  on  a  series 
of  changes  which  tho  phosphates  and  carbonatirs  ia:i  undergo, 
when  acids  itr  alkalies  are  added  to  solutions    ontaining  them, 


I 


ii 


50 


PHYSIOLOGY    FOR   DKNTAI-   STIDKNTS. 


witliout  causing  any  coiisidcinbl.'  aiiiomit  of  fm-  H-  or  Oll-ioii  to 
be  set  fm'.  This  has  Ihmmi  calh-d  Uw  "biiffrr  aclioii"  of  such 
salts.  It  endows  tin-  saliva  with  the  power  of  locking  away  con- 
siderable (juaiitities  of  acid  or  alkali. 

Tn  actually  measuring  the  neutralizing  power  of  saliva,  it  i.s 
best  first  of  all  to  bring  the  saliva  to  a  definite  Il-ion  concentra- 
tion by  adding  standard  acid  an<l  then  to  find  out  how  much 
alkali  is  recpiired  to  bring  it  to  another  definite  Il-ion  concentra- 
tion. 

The  metlio<ls  for  applying  the  above  princij)les  are  as  follows: 
10  c.c.  .ssdiva  is  diluted  in  an  evajmrating  disl  with  20  c.c. 
water  which  has  been  boiled  to  e.xpel  ('()„  and  then  cooled  to 
20°C.  About  eight  drops  of  an  a(|ueous  solution  of  paranitro- 
])Iienol  is  then  added  and  N  200  IK'l  run  in  from  a  burette,  with 
constant  .stirring  until  the  yellow  color  due  to  the  indicator  ju.st 
disappears.  The  amount  of  N  200  IK'l  is  noted.  N,  200  MI^IIO 
is  then  added  till  the  yellow  color  just  returns.'  The  difference 
between  the  two  readings  gives  the  alknliuity  in  tern  s  of  c  c  of 
N;  200  IIC'I. 

The  aculitti  may  be  directly  measured  by  adding  four  drops 
of  an  alcoholic  .solution  of  phenolphthalein  to  another  10  c.c. 
sample  of  saliva  and  running  in  X  200  \a()II  until  a  tlefinite 
l)ink  color  results. 

Addition  of  the  acidity  and  alkalinity  results  gives  the  total 
neutralizing  j»ower  of  the  saliva,  or  in  other  words  the  power  of 
maintaining  neutrality.  This  is  a  much  more  con.stant  property 
of  saliva  than  the  acidity  or  alkalinity  alone,  and  it  has  conse- 
(|uently  been  u.sed.  in  the  most  recent  work  of  Mai-shall,-  for  the 
purpose  of  ascertaining  u'h<th<r  ihi  susccptibUiiy  to  drntal  ai- 
rir.s  brars  ain/  nlatioiiship  to  th(  rant  ion  of  the  xalini.  It  was 
found  that  it  does  not.    On  the  other  hand,  this  author  has  .shown 


irhe  rea.s(.n  for  titiHtiiis  hjuk  with  N  L'(ii»  .\H,HO  tiU  a  yellow  color  again 
rpapppaiw  w-hen  measuriiiK  the  alkalinity,  is  to  inrreasp  the  accuracy  of  the 
titration,  it  being  often  Jifflcult  to  decide  the  point  at  which  the  color  rfisan- 

,^h   1 ,1  ^S.*"*<    '"   "S»'<1-     >"»<»H   1.S  employed   in   the   acidity   titration   becaus.. 
phenolphthalein  cannot  be  u«ed  with  ammonia. 

2Cf.  J.  A.  Marshall,  Amer.  Jour,  of  Physiology,   191.''i,  XXXVI.  p    260. 


CHEMISTRY    OP    SALIVA. 


51 


that  tho  neutralizing  power  of  siiliva,  eoUeeted  without  any  ef- 
fort or  artificial  stinmhttion  of  the  nioutli  (resting  saliva),  is 
very  distinctly  less  than  that  of  sjiliva  collected  whilst  chewing 
on  a  i)iece  of  paraitin  (activated  saliva),  ai\d  that  this  difference 
becomes  virtf  much  ](.ss  in  thosi  with  rarioKs  hilh.  Marshall 
has  suggested  that  we  shoidd  express  the  ratio  of  the  neutraliz- 
ing power  of  resting  saliva  to  that  of  activated  saliva  as  a  per- 
centage ratio,  which  he  calls  the  sdlirarj/  factor.  In  persons  im- 
mune from  caries  this  factor  amounted  to  4:{-S0;  in  those  with 
caries  it  varied  from  H0-l;{2.  The  following  examples  will  illus- 
trate these  points: 


NOBMAI.   RESTING    SALIVA 


ACTIVATED  SALIVA 


Case 

c.  e. 
N  200 
HCI 

c.  c. 
N/200 
NaOH 

Neutral- 
izinr 
Power 

c.  c.     ~ 
N  200 
HCI 

c.  c. 
N,200 
NaOH 

N.iitral- 
Power 

Salivary 
Factor 

No. 

22.22 

7.60 

29.82 

57.55 

0.90 

58.45 

51 

canes 

Carious 
Without 

18.50 

7.00 

25.50 

22.80 

2.13 

24.93 

102 

care 

If  those  interesting  (>l>sei'vations  should  prove  to  be  confirmed 
by  other  observers,  it  will  supply  us  with  a  comparatively  simple 
method  for  -olving  what  has  hitherto  been  a  most  i)uzzliiig  ques- 
tion  and  which  has  i)rompted  several  observers,  particularly 
Hunting  and  Price,  to  employ  the  very  delicate  physico-chemical 
methods  of  the  concentration  cell  (p.  M  )  anil  electrical  conduc- 
tivity to  its  elucidation. 

Before  leaving  the  subject  of  the  relationship  between  the 
character  of  the  saliva  and  the  occurrence  of  dental  caries,  it 
may  be  well  to  point  out  that  other  factois  besides  the  neutral- 
izing power  of  the  saliva  must  be  taken  into  con.sideration,  name- 
ly, its  amount  and  the  presence  of  phosphates.  A  large  and  free 
flow  of  saliva,  besides  mechanically  cleansing  the  teeth,  will  offer 
more  neutralizing  fluid.  An  e.xcess  of  phosphates,  on  the  other 
hand,  will  encourage  fermentation  of  any  carbohydrate  which 
may  be  adherent  to  the  teeth  and,  by  forming  acids,  thus  tend  to 
erode  the  t4»eth  and  predispose  to  caries. 


!  f 


52  PHYSIOLOGY   FOR   DENTAL   STUDENTS. 

Tartar  Fonnation  and  Salivary  Calculi.— Under  certain  con- 
ditions a  precipitate,  varying  in  color  from  pale  yellow  to  almost 
black,  collects  on  the  teeth,  particularly  on  the  lower  incisors 
and  molars.  This  precipitate  is  called  tartar,  and  it  may  be 
either  hard  (as  on  the  incisors)  or  soft  (as  on  the  molars).'  Its 
chemical  composition  varies  considerably,  but  may  be  given  as 
follows : 

T  II 

Water  and   organic   matter 32.24  per  cent        31.48  per  cent 

Magnesium  phospliate o.98  per  cent         4.91  per  cent 

Calcium  phosphate  63.08  per  cent        72.73  per  cent 

Calcium  carbonate  3.7  per  cent        

(Talbot) 

The  organic  matter  consists  of  epithelial  scales,  other  extran- 
eous matter  and  leptothrix  chains.  The  place  and  manner  of 
deposition  shows  clearly  that  the  tartar  is  largely  derived  from 
the  .saliva,  the  chemical  explanation  of  the  precipitation  being 
probably  as  follows :  Saliva,  as  it  is  produced  in  the  gland,  con- 
tains calcium  bicarbonate,  which  is  soluble  in  water,  and  is  pre- 
vented from  changing  into  the  insoluble  carbonate  by  the  pres- 
ence of  free  carbon  dioxide  in  solution.  When  the  saliva  is  di.«i- 
charged  into  the  mouth  some  of  the  carbon  dioxide  escapes  from 
it  80  that  the  bicarbonate  changes  to  carbonate  and  becomes  pre- 
cipitated. The  precipitate  carries  down  with  it  phosphates  as  well 
as  any  organic  debris  or  mico-organisms  that  may  be  present. 

The  precipitation  of  calcium  carbonate  may  even  take  place 
in  the  salivary  ducts  (Wharton's),  thus  forming  salivary  calculi, 
which  may  reach  the  size  of  a  pea  or  larger.  Such  calculi  may 
contain  as  much  as  3.8  per  cent  of  organic  .natter,  the  remainder 
being  largely  calcium  carbonate.  The  following  table  gives  the 
composition  of  three  such  calculi : 

r.  ,  .                                         '  "                           I" 

Calcium  carbonate   81.2  per  cent  79.4  per  cent        80.7  per  cent 

Calcium  phosphate   4.1  per  cent  5.0  per  cent          4.2  per  cent 

Magnesium  phosphate  ...    .  present 
Organic  matter  and  other 

soluble  solids 13.3  per  cent  13.3  per  cent        13.4  percent 

^*'®'' 1.3  per  cent  2.3  per  cent         1.7  ,er  cent 

(T«lbot) 


CHAPTER  V. 

DIGESTION  (Cont'd). 

Mastication:  Deglutition:  Vomiting. 

Mastication. — By  the  movpmonts  of  the  lower  jaw  on  the 
ujiper,  the  two  rows  of  teeth  come  together  so  as  to  serve  for  bit- 
ing or  crushing  the  food.  The  resulting  eomipinution  of  the  food 
forms  the  first  step  in  digestion.  The  manner  of  occlusion  of  the 
cusps  of  the  teeth  in  the  performance  of  this  act  is  not  a  problem 
of  Physiology,  but  rather  of  Anatomy  and  r)rthodontics ;  never- 
theless, the  other  factors  whicii  '-ontribute  to  the  efficiency  of  the 
process  and  the  condition  into  which  tlie  food  is  brought  by  it 
are  subjects  to  which  we  must  devote  some  attention.  The  up 
and  down  motion  of  the  low»'r  jaw  results  in  biting  by  the  in- 
cisors, and  after  the  mouthful  has  been  taken,  the  side  to  side 
movements  enable  the  grinding  teeth  to  crush  and  break  it  up 
into  fragments  of  tlie  j)roper  size  for  swallowing.  Tlie  most  suit- 
able size  of  the  mouthful  is  about  five  cubic  centimetres,  but  this 
varies  greatly  with  habit.  After  mastication,  tlie  mass  weighs 
from  3.2  to  6.5  grammes,  about  one-fourth  of  this  weight  being 
due  to  saliva.  The  footl  is  now  a  semi-fluid  nnish  containing  par- 
ticles which  are  usually  less  than  2  millimetres  in  diameter. 
Some,  however,  may  measure  7  and  even  12  millimetres. 

Determination  of  the  proper  degree  of  fineness  of  the  food  is  a 
function  of  the  tongue,  gums  and  cheeks,  for  which  purpose  the 
mucous  membrane  covering  them  is  supplied  with  vei-y  sensitive 
touch  nerve  endings  (see  p.  244).  The  .sensitiveness  of  the 
tongue,  etc.,  in  this  regard  exi>lains  why  an  object  which  can 
scarcely  be  felt  by  the  fingers  seems  to  be  <|uite  large  in  the 
mouth.  If  some  particles  of  food  that  are  too  large  fnr  swallow- 
ing happen  to  be  carried  backward  in  the  mouth,  the  tongue  re- 
turns them  for  further  mastication. 

The  .saliva  assists  in  mastication  in  several  ways:  (1)  by  <lis- 
.solving  some  of  the  food  constituents;  (2)  by  partially  digesting 

53 


54 


I'UVMULCKJV    n»K    PKNTAL    i-TlDKM'S 


Ir 


sonic  of  tlic  starcli ;  (.'})  by  softciiingr  th«>  mass  of  food  so  that  it 
is  nioro  ivadily  crushed;  (4)  by  covering  the  holus  with  mucus 
so  as  to  make  it  more  readily  transferabh-  from  place  to  place. 
The  secretion  of  saliva  is  therefore  stimulated  by  the  chewing 
movements,  and  its  composition  varies  according  to  the  nature 
of  the  food  (p.  i'l).  In  some  animals,  such  as  the  cat  and  dog, 
there  is  no  mastication,  coating  of  the  food  with  saliva  being  the 
only  change  which  it  undergoes  in  the  mouth.  In  man  the 
ability  thus  to  bolt  the  food  can  readily  be  ac<|uired.  not  however 
without  .some  detriment  tc  t';e  efficiency  of  digestion  as  a  whole. 
Soft  starchy  food  is  little  chewed,  the  length  of  time  required 
for  the  n.a.stication  of  other  foods  depending  mainly  on  their 
imture,  but  also  to  a  certain  degree  on  the  appetite  and  on  the 
size  >f  the  mouthfid. 

The  crushing  foire  of  the  molai-s.  as  measured  by  a  dyna- 
mometi-r.  has  been  found  to  rise  as  high  as  270  pounds,  which  is 
far  in  excess  of  the  force  re<(uired  to  crush  the  ordinary  foot! 
.stuff.s.  Thus  cooked  meats  have  a  crushing  point  which  varies 
between  1.")  and  SO  i)ounds  on  direct  thrust,  but  is  considerably 
less  when  there  is  a  side  to  side  movement,  as  there  is  in  chewing. 
Candies  have  a  crushing  point  of  AO  to  110  pounds,  and  inits 
.").")  to  170  pounds.  Admixture  of  the  foo<l  with  saliva  greatly 
lowers  the  crushing  point,  esi)ecially  in  the  case  of  such  foods  as 
soft  bread.  Without  such  admixture  this  hardens  into  a  solid 
mass  when  it  is  crushtnl,  whereas  it  readily  breaks  up  into  small 
particles  in  the  i)resence  of  saliva. 

It  cannot  be  too  strongly  insisted  upon  that  the  act  of  ma.sti- 
cation  is  of  far  more  importance  than  merely  to  break  up  and 
prepare  the  foo<l  for  swallowing.  It  caust's  the  food  to  be  moved 
about  in  the  mouth  so  as  to  develop  its  full  effect  on  the  taste 
buds;  the  crushing  al.so  rclea.ses  odors  which  stuuulates  the  ol- 
factory epithelitun.  On  these  stimuli  depend  the  .satisfaction 
and  pleasure  of  eating,  which  in  turn  initiate  the  process  of  gas- 
tric digestion  (s«'e  |>.  (iO).  Thus  it  lias  been  ob.stTved  in  cliil- 
divn  with  ga.stric  fi.stuhe  that  the  chewing  of  agreeable  l,M)d 
caused  the  ga.stric  juice  to  be  actively  seereted,  which,  however, 
was  not  the  case  when  tasteless  material  was  chewed. 


DEOLITITION. 


55 


Tbo  benefit  to  digestion  as  a  whole  of  a  large  secretion  of  sa- 
liv  .  brought  about  by  persistent  ehewing.  has  been  assumed  by 
some  to  be  mueh  greater  tiian  it  really  is.  and  tliere  has  existed, 
and  indeed  may  still  exist,  a  sehool  of  faddists  who.  by  deliber- 
ately ehewing  far  beyond  tlie  neeessary  time.  imagiiM'  themselves 
to  thrive  better  on  less  food  than  tiiose  who  oeeupy  their  time 
with  other  more  profitable  pursuits. 

Deglutition  or  Swallowing. — After  being  masticated  tiie  food 
is  rolled  up  by  the  tongue  acting  against  the  palate  into  a  bolus, 
and  this,  after  being  lubricated  by  saliva,  is  moved,  by  elevation 


I 
f  ■ 


Kijf.  4, — 'Phf  ihiinms  which  tiikc  iilaii  in  the  iiDSitiiiii  of  tlif  niut  of  tlic 
tciiiguc,  th»"  .soft  puliitf.  the  f|iiKli>ttis  and  tlic  Imivmx  duriiiK:  thi>  seiond  statfi' 
of  swallowiMK.  The  thick  dotted  line  indicates  the  |)<wition  during  swal- 
lowing' 

of  the  front  of  tiie  tongue,  towards  the  back  of  tlie  mouth.  This 
constitutes  the  first  slitfft  of  swallowing,  and  is,  so  far,  a  volun- 
tary act.  AlKiut  this  time  a  slight  inspiratory  c(»iitraction  of  the 
(iiai)hragin  occurs — the  so-called  respiration  of  swallowing — and 
the  mylohyoid  (the  muscles  of  the  fioor  of  the  mouth)  (juickly 
contracts  with  the  conseciuence  tiiat  the  bolus  passes  between  the 


56 


PHYSIOLOGY  FOB  DENTAL  STUDENTS. 


pillars  of  the  fauces.     This  marks  tlie  beKinning  of  tlie  second 
stage,  the  first  event  of  which  is  that  tlie  bolus,  bv  stinuilating 
sensory  nerve  endings,  acts  on  nerve  centers  situated  in  the  m,.- 
dulla  oblongata  so  as  to  cause  a  coordinated  scries  of  movements 
of  the  muscles  of  the  pharyn.x  and  larynx  and  an  inhibition  for 
a  moment  of  the  respiratory  center  (p.  21!)).     The  mov.-ments 
alter  the  shape  of  the  pharynx  and  of  the  various  openings  into 
It  in  such  a  manner  as  to  compel  the  bolus  of  food  to  pass  into 
the  .esophagus:  (see  Fig.  4)   thus.   (1)   the  soft  palate  becon.es 
elevatcl  and  the  posterior  wall  of  the  pharynx  bulg.-s  forwar.l 
so  as  to  shut  off  the  posterior  nares.  (2)  the  posterior  pillars  of 
the  tauees  approximate  so  as  to  shut  off  the  mouth  cavity   and 
(3)  in  about  a  tenth  of  a  .second  after  the  mylohvoid  has  con- 
tracted, the  larynx  is  pulled  upwards  and  forwards  under  the 
root  of  the  tongue,  which  by  being  drawn  backwards  becomes 
banked  up  over  the  laryngeal  opening.     This  pulling  up  of  the 
larynx  brings  the  opening  into  it  near  to  the  lower  half  of  the 
dorsal  s.de  of  the  epiglottis,  but  the  upper  half  of  this  structur.. 
projects  beyoml  and  s.-rves  as  a  le.lge  to  gui.le  tlie  bolus  sufelv 
past  this  critical  part  of  its  cour.se.     (4)  To  furtlier  .safeguard 
any  entry  of  food  into  the  air  pa.s.sages,  the  laryngeal  opening  is 
narrowed  by  approximation  of  the  true  and  false  vocal  cords 

The  force  which  propels  the  bolus,  so  far.  is  mainlv  the  con- 
traction of  the  mylohyoid,  assisted  by  the  movements  of  the  root 
of  the  tongue.  When  it  has  K.iched  the  lower  end  of  the 
pharynx,  however,  the  bolus  rea.lily  falls  into  the  oesophagus 
which  has  become  dilated  on  account  of  a  refl.'x  inhibition  of  the 
constrictor  muscles  of  its  upper  end.  This  so-called  second  stage 
of  swallowing  is  therefore  a  complex  coordinated  movement  ini- 
tiated by  afferent  stimuli  and  involving  reciprocal  action  of 
various  groups  of  mu.scles:  inhibition  of  the  rcspiratorv  muscles 
and  of  those  that  constrict  the  .esophagus,  and  stimidation  of 
those  that  elevate  tlie  palate,  the  root  of  the  tongue  an.l  the 
larynx.    It  is  jiurely  an  involuntary  i)roeess. 

The  third  stag,  of  deglulilion  .'(insists  in  the  passag*'  of  t!ie 
swallowed  food  along  the  .esophagus.  The  way  in  which  this  is 
done  depends  very  much  cii  the  physical  consistence  of  the  food 


DEGLUTITION, 


Ot 


A  solid  bolus,  that  nioro  or  less  fills  the  a'sophaKus,  excites  a 
typical  peristaltic  wave  which  is  chai'acterized  by  a  dilatation 
of  the  oesophagus  iniinediately  in  front  of.  and  a  constriction 
over  and  behind  the  bolus.  Tins  wave  travels  down  the  opsopha- 
gus  at  such  a  rate  that  it  reaches  the  cardiac  sphincter  in  about 
five  or  six  .seconds.  On  arriving  h(>re  the  cardiac  sphincter, 
ordinarily  contrar  >  ;1.  relaxes  for  a  moment  .so  that  the  bolus 
pa.sses  into  the  stomach.  The  peristaltic  wave  travels  much  more 
rai)idly  in  the  upper  portion  of  the  oesophagus  than  lower  down 
because  of  differences  in  tlic  nature  of  the  muscular  coat,  this 
being  of  the  striated  variety  above,  and  of  the  non-striated,  be- 
low. The  purpose  of  more  rapid  movement  in  the  upper  portion 
is  no  doubt  that  the  bolus  may  be  hurried  past  the  regions, 
where,  by  distending  the  o'sophagus,  it  might  inttn-fere  with  the 
function  of  neighboring  structures,  such  as  the  heart.  The  peris- 
taltic wave  of  the  o'Sophagus.  unlike  that  of  the  intestines  (see 
\).  7!)),  is  transmitted  by  nerves,  namely,  by  the  oesophageal 
branches  of  tiie  vagus.  ]f  these  be  severed,  but  the  muscular  it- 
self left  intact,  tlie  (esophagus  becomes  dilated  above  the  level 
of  the  section  and  contracted  below,  and  no  peri.staltic  wave  can 
pass  along  it ;  on  tiie  other  hand,  the  muscular  coat  may  bo  sev- 
ered (by  cru.siiing,  etc.)  but  the  peristaltic  wave  will  jump  the 
breach  provitled  no  damage  has  been  doJic  to  the  nerves. 

The  propagation  of  the  wave  by  nerves  indicates  that  the  sec- 
ond and  third  stages  of  deglutition  must  be  rehearsed,  as  it  were, 
in  the  medullary  nerve  centers  from  which  arise  the  fibers  to  the 
pharynx  and  the  different  levels  of  the  oesophagus.  The  afferent 
stinudi  which  initiate  this  process  proceed  from  the  pharynx  by 
the  fifth,  superior  laryngeal  and  vagus  nerves  and  not  at  all 
from  the  o'sophagus  it.self ;  thus,  a  foreign  body  placed  directly 
in  the  (esophagus  remains  stationary,  but  innuediately  begins  to 
move  if  the  pharynx  be  stimulated,  as  by  touching  it.  The  af- 
ferent fibers  in  the  glossopliaryngeal  nerve  exercise  a  powerful 
iiilnbitonj  influence  on  the  deglutition  center  as  well  as  on  that 
of  respiration.  Thus,  if  swallowing  movements  be  exeited  by 
stinudatiug  the  central  end  of  tlie  superior  laryngeal  nerve,  they 
can  be  instantly  inhibited  by  simultaneously   stinuilating   the 


oS 


I'llYslOUKiV    FOK    DKNTAI,    STI  DKNTS 


i  I'i 


Klossopl.a,..vn«..al.  an.l  the  ,vspir„to,y  ,„ov,.„u.„ts  stop  i„  wl.at 

ever  position  th.-y  ,„ay  ha  v.  h....„  i„  „t  the  ti,„e 

This  inh.hition  of  the  .esopha^nis  is  i.„i....,,  «  „„„t  important 
art  ot  the  p,.„ees.  when  li.ni.i  or  snui-IU^ui  food  is  swiuowed 

I  >   the  eontraet.on  of  the  n.yh.hyoi.l  mnsele.  tJui.ls  are  ..uick 

•shot  down  the  .liste.ul. sopha^ns.  at  the  h,we,.  en     of  w.ie 

on  aeeonnt  of  the  eardiae  sphineter  hei,.,,  elosed.  they  1  -Lnu ht e" 
""t.I  t   e  „,.rival   of  the   peHstaltie  wave  whieh   l^ili:::; 

>-"  set  up  by  stnnnlation  of  the  pharynx.     If  the  swallow     I 
■'"""'diately  .vpeate.l.  as  is  „s„ally   the  ease   in   drinkin.!    t," 
-opha,..s  remains  dilated  beean.-  peristalsis  is  inhibite.r  „i   1 

These  faets  have  been  revealed  by  listenin.r  with  a  stetheseo,,e 

i^  the  sounds  pro<iuee,i  by  swallowin...  an.l  by  observing  with     n 

X-ray   lamp   the   shadows   produeed   along   the   eourse   of   the 

u-sophag^  when  food    i.npregnate.l  with  bismuth  subnitrate 

..ken      When  a  sol„l  1h,1„s  is  swallowed,  one  soun.I  is  usaallv 

'■ard,  but  w,t     li,uid  foo,l  there  are  two.  one  at  the  u   pe 

.  ud    hear.1  over  th,.  epigastrium)  some  four  or  six  seeonds  later 
.l»e  to  the  arrival  here  of  the  peristaltic  wave  with  the  ac.      -" 
panynig  opening  of  the  eardiae  sphincter  an.l  the  escape  of  te 
fluid  aiHl  air  into  the  stomach.    Sometimes,  as  when  tl  e  plon 
IS  in  the  horizontal  position,  this  s,.eon.l  sound  mav  be  brok^M   up 
1^0  severa     uidieating  that.  una..siste.l  by  gravity',  the  m  i     dl 
"O    so  readily  pas.s  through  the  sphincter.     The  X-rav  shadows 
ndik  a::rr'^  -conformity  with  the  above.     After  swall  J^:; 
"Ilk  ami  bismuth,  for  example,  the  .shadow  falls  quicklv  to  the 
lower  end  of  the  .esophagus  an.l  th.-n  slowly  into'th.   i.  a 
When  the  passag,.  of  a   .soli.l   bolus  is  watche.l   bv   the   X  n v 
".etho<l    Its  rat.,  of  .!..,sc..i,t  will  be  f.Hui.l  to  .lep..nd  on  whether 
orno.t,sw..,M„bri..at...,wit 

'st:;x:::;;:,r  ^'•'''' • '•«•'- ^^^ -..<>*- '-.-o,.- 

The  Act  of  Vomiting.-Tl.is  is  usually  pre..ed..d  bv  a  IVeling 
of  sickness  or  uausc.  and  i.s  i.u.iated  by  a  very  activ'c  scretidn 


VOMlTlNti. 


59 


of  saliva.  The  saliva,  mixed  with  air,  accumulates  to  a  consider- 
able extent  at  the  lower  end  of  the  (psophagus  and  thus 
distends  it.  A  forced  inspiration  is  now  made,  during  the 
first  stage  of  which  the  glottis  is  open  so  that  the  air  enters 
the  lungs,  but  later  the  glottis  closes  so  that  the  in- 
spireil  air  is  sucked  into  the  (esophagus,  which,  already 
somewhat  distended  by  saliva,  now  becomes  markedly  so.  The 
abdominal  muscles  then  contract  so  as  to  compress  the  stomacli 
against  the  diaphragm  and,  simultaneously,  the  cardiac  sphincter 
relaxes,  the  head  is  held  forward  and  the  contents  of  the  stonmch 
are  ejected  through  the  i)reviously  distended  n'sophagus.  The 
compression  of  the  stonmch  by  the  contracting  abdominal  mus- 
cles is  assisted  by  an  actual  contraction  of  the  stonmch  its«>lf, 
as  has  been  clearly  demonstrated  by  the  X-ray  method.  (See  p. 
58.)  After  the  contents  of  the  stomach  itself  have  been  evac- 
uated, the  pyloric  sphincter  may  also  relax  and  thus  permit  the 
contents  (bile,  etc.)  of  the  duodenum  to  be  vomited. 

The  act  of  vonuting  is  controlled  by  a  center  located  in  the 
medidla,  and  the  affcrriit  fibers  to  this  center  may  come  from 
many  different  regions  of  the  Iwdy.  Perhai)s  the  most  potent 
of  them  come  from  the  .sensory  nerve  endings  of  the  fauces  and 
j)harynx.  This  explains  the  tendency  to  vomit  when  the  mucosa 
of  this  region  is  mechanically  .stimulated.  Other  atferent  im- 
pulses come  from  the  mucosa  of  the  stonmch  itself,  and  these  are 
stimulated  by  swallowing  certain  drugs  called  emetics,  import- 
ant among  which  an-  strong  salt  solution,  mustard  water,  zinc 
sulphate,  etc.  When  some  poisonous  s\ibstance  has  been  swal- 
lowed, the  immediate  treatment  is  to  give  one  of  these  emetics 
and  thus  cause  the  poison  to  be  vomited.  Certain  other  emetics, 
particularly  tartar  emetic  and  apomorphine,  act  on  the  vomiting 
center  itself,  and  can  thei-efore  act  when  given  subc\itaneously. 
Afferent  vomiting  imj)uls«'s  also  arise  from  the  abdominal  vis- 
cera, thus  explaining  the  vomiting  which  occurs  in  strangulated 
hernia,  and  in  other  irritative  lesions  involving  this  region. 


CHAPTER  VI. 

DIGESTION  (Cont'd). 

Digestion  in  the  Stomach. 

The  Secretion  of  Oaatric  Juice.— After  nass„no.  «!.,.        i 
.>hi.^,  ..e  foo.,  eo„.t.  i„  the  ^.n.nZ  TZ:l  'tZ 
\lo\7!      '"-""f  «•"'•>'  it  l.H.ome.s  dispo..cl  in  definite  layers 

center.    W  hen,  as  ,h  usual  in  n.an,  the  food  is  more  or     • .  fluid 
th.s   ayer  formation  is  less  evident  and  it  eolleets  in  f      alst 
pendent  part  of  the  body  of  the  stomach  (see  Fig.  5)      vSi    a 
few  m.„ut.s  of  the  entry  of  the  first  portion  of  Ll   the  ghl,: 
of  the  gastrie  mucosa  begin  to  seerete  their  digestive  juiees   The 
unn.ed,a  e  exc.ting  cause  of  this  secretion  is  Lt  the    o,  act  o 
ioo.l  w^h  the  mucosa-although  this  acts  later-but  i    a    ..  r 
vous  st.n.ulus  trans„.itte.l  to  the  ston.aeh   through   tl  vag.  s" 
iK-rve.  and  c.„„ng  fron.  a  nerve  center  situated  in  the  medX 
The  ac^v^Uc,  of  th,s  ,j„stru-  center  are  called  into  operation  h, 
afferent  „„p„,,,,.    ,  ,,,  „,,,.^^.  ,,^^,  ,^^^^^.^^^^^    .^  th    tast^M. 

ond  o  factor,  epukclU.n.     The  process  of  gastric  secretion 
therefore  H„t,ated  in  the  mouth,  and  the  stimulus  that  i     r 
sponsible  for  U  ,s  the  good  taste  and  the  flavor  of  the  fo^     ,Zt 
as  in  the  case  of  the  salivary  glands,  the  foo<l,  in  orderTo  exc  t 
he  secrefon,  need  not  actually  enter  the  mouth  for  a  psycho^o^ 
cal  stimulus  may  also  act  on  the  gastric  center.    Thus    he  ilt 
o    sn.ell  of  savory  food,  or  even  the  hearing  of  son,e  sound,    f 
known  by  experience  to  be  associated  with  the  gratificat  o     o 
the  appetite  can  call  it  forth.    These  important  f  "t    w    r^rs 
o   all  revealed  by  observations  through  a  gastric  fistula  made  i 

t.,^e^d  by  the  n.outh  because  of  .stricture  of  the  u>sophag„s  ■ 

^Arter  outtln.  th.  v.,,  this  .....u.n  „r  .a.tric  Jui..  au.«  not  occu. 

60 


DIGESTION   IN   THE   STOMACH. 


Gl 


ln'  had  to  ]h'  fed  tliroiiKli  tli<»  f^astrii;  fistula,  but  vvlicii  ln>  was  al- 
lowed to  <'how  food  for  \vhi«'li  lit*  had  a  rolish  and  tlu'ii  spit  it  out. 
(i^astric  socretion  ot-curn-d.  Tills  obwrvation  s>igK«'''tt'd  to  I'aw- 
low  the  establisliment  of  analogous  conditions  in  dogs,  with  tlic 
modification  that,  besides  the  fistula  in  the  stomach,  one  was 
made  of  the  oesophagus  in  the  neck  in  s\ich  a  way  that  swalloAved 
food  escape<l  by  it.  The  animal  could  therefore  swallow  inter- 
minably without  ever  l)eeoming  satisfied,  and  it  was  observed 


KiB.  5, — Diasrums  of  outline  and  position  of  stomaih  a«  indi(  att-d  '  >  skla- 
Kianis  taken  on  man  in  the  erect  position  at  intervals  after  swallowing  food 
impregnated  with  liismuth  subnltrate.  A,  moderately  full ;  li.  practieally 
empty.  The  clear  space  at  the  upper  end  of  the  stomach  is  due  to  ga.i.  and 
it  will  lie  noticed  that  this  "stomach  bladder"  lies  close  to  the  heart.  (T. 
Wingate  Todd.) 


tliat  when  it  did  so,  gastric  juice  flowed,  provided  this  "sham 
feeding"  wa.s  with  appetizing  food.  Stones,  bread,  acid  or  irri- 
tating substances,  although  they  might  cause  much  saliva  to  be 
seereteil  and  swallowed  (see  p.  4'?),  had  no  influence  whatso- 
ever on  the  fiow  of  gastric  juice.  The  only  adequate  stimulu!^ 
was  gratification  of  the  appetite. 


«2 


I'MV-lul    "   \     r.  ,i{    1)1    xT^,,    sTIDKNTs. 


In  f.assih^f.  „  M«y  Im  m-II  to  rail  i.ff.Mtion  t„  th.-  pra.h.al 
inipuifi.n..,.  of  tlM.s,-  olw,  .  .41,  „.s  i„  -.,iMM-.-tioii  with  the  f.-.-dinu 

«l  <h.l)ilitat.Ml  |HrN..hs:  l.y  in    ,i.-i.t  i 1,,^  with  app.tizii.K  f.Hnl 

" ot'-'tioMHl  .on.lition  in  lik.L.  • .,  i,„,,rov,-  nmch  nn.tv  rapidly 

than  by  o.-«.asi.,i.al  sfiitti.iK  «ii      Mii<-oinf.  nial  n.xtuivs.  how.'v.-r 
rich  thcw  may  li<-  in  talont-s  ai.l  nitntjfcn 

Th..  m-crvtion  is  th..n'fon.  w.-ll  narih-.l  th.-  ,//>/W<7,  ju,,,,  ainl 
It  lasts  sonu'tini.-s  for  n.arlv  iw..  hours  aft.-r  sham  fWdin^  h  ■< 
Ix-n  .l.scontiiMi.Ml.  V.-t  this  is  ..nh  ahoiit  on.  half  as  lon^  as  th- 
tun.'  .lunnK  which  KHstri,-  juic,-  is    ..cictcl  when  tiic  f.XMl  is  ac 


FiK.    fi._i)iaK,aii 
from  till'  iniiiii  stm 


....  •'    "'"marh    shi.winK    miiiiai  Ktom:     h    (S)    «..pa 

...I  th..  ma.M  .si„„,a,.h   .  l)    by  a  ,l.,ul.I..  lav.-r  ..f     .,.j.-, 
the  oi).ninK  ..I    th.-  i>.,uch  on  th.-  abdominal  wall 


.)us  iH<-ml>nin.       t 
1  awlow    I 


tiially  i)crmittc(l  to  •  ut-r  the  stomach 
tfii  vaii.sf  of  fht  <<n,li,nn(l  snntio,  t 
some  means  by  m  !u<h  the  jfastrie  j, 
mixed  with  footl,  whil  normal  dipcstm 
inp  no  duct  the  only  mean-  by  which  ti 
isolating  a  portion  of  the  stomach  as  a 
exteriorly  throufrh  which  th-  secretions 
removed.  An  operation  for  maki!!j»  sue! 
stomach,"  as  it  is  called,  without  injuring  an\ 


'  II  .Ji'tler  to  inve>'iea 
V    s  iiecessa-      to  u- 

-n-.-ted.  I, 
^lyf  -ss,     Ha\ 

do 


illd  be 

as  ill  '» 
.'Oiili! 
'Uch  w 

■etin^' 

I, 

inj-.- 


was  b\ 
ning 

i  h.. 
ature 
OS  of 


IH«iK>T"     N     i\ 


.'il 


i  iiM  \<  II. 


nil 


til  tilt' 

■  rt.T 

M. 


'  111 


till    >toiii.     ll  llHN  Idcll  .li\    -     .    In  wlow  Kiu     (!').  III- 

iilliiiM  oii>. ctllcctiii!,'  till       net  iiDiii       I'  niiiiii  stoMiii        iiul 

til'  iiiliijit  i-fstiilii  ll  iifli  •  slwllii  I'ljiin;  \v;is  fitniul  til.:  tllt'.v 
i.iii  si  -icli  |iMl'iil'  vitli  '  ■  iiiinthcr.  ill  itiiiit  as  well  s  iu 
■ti-i'iiirfli  "  !«MTctHii  Th.  M'ci-ftioii  ill  tl.  ininiatiii-i'  stm  lacli 
lln'ivf<"  .■  ■iir;ii  '\  iiiiri'dr^  •Iii'  si'ci'ctioi.  inM-iii-rinir  'm  th.-  ;;in 
>l(tnifi(       aii.l  s<      •  riiiits  lis  to  stinlv    this  ,>  Ihmi  I'ikkI   is  ;,   luall' 

Iwiiijr  iti>ri"*'t'<l 

Hv    ititriMJiKMi.j.'  t'ood  (iircctly  into  tlit-  iiiiiin    -toinacl'   '      ..,,  'Ii 
.1  ■  -liiia,  it  w;.-.  'tMiiKl    l)v  oliscrvatioiis  on  tiif  sft    rtii. 
Ill        itiirc  -    una.  h,  tli.it  Verv  litti''  sirrctii       dcciioiMi 
soiin-  tiiiu'.  iro\  iiif-il  of  course  that  |in'cautioiis      kI 
as  by  fxp     iin-iitiiijr     n  a  sh-cpiiin  animal,  not  to        i 
tite  juici       'I'hiTi    w        'uiiiid   to  ln'  trrcat  (lis<'ri 
natiirp  of  tl  c  ,ulfijna         iiiiuhis  for  this  Ux-al  n  en 
oa!    nnii  latioii  of  the  -..-trie  iiiiico.sa.  contact  v 
Si  In  Sill     a.  or  witii  white  of  ejfjr.  failed  to  n 

tin:     water  mu    a  slisrlit  efTect.  milk  still  '   on 
M'cr-  ti.-!i  oi<     rrcil  when  a  dccoctinii  o|   ,      ,t 
a  .soln      II  .-.nttaiiiii!,'  the  half  dijrested  jii 
tii>'  'h  ,       Wittes  peptone)    was  phK-en 

It  was  i.r  olisifved.  when  meat   was  (inectly  jilacrd  in  the 

stomach  ■■  it  the  juice  which  collected  in  the  pouch  increased, 
both  ill  qu.iitity  and  in  streiijrth.  after  tl  first  hour,  ai  I  that 
it  continued  to  flow  even  after  four  h  ii-  us  indicatiii}?  that 
til.    primary  stimulus  had  come  from  t  la -tives  in  the  meat, 

iuit  that,  as  the  protein  of  the  meat  ,  .uiie  diKt'stci.  further 
stiniuJatioii  o<'curred  on  account  of  the  proteose  and  jieptones 
liberated. 

This  local  sliiiiiiliifioii  is  imlependeiit  of  flic  iiMiinJIarv  nerve 
center  that  controls  secretion  of  the  appetite  juice,  for  •  stili  (m-- 
curred  after  both  vapi  liad  beei  divi  ''d  or  even  after  destruc- 
tion of  the  .symiiathetic  nerve  pei-.uw's  m  the  .ilMlomen.  It  (iiiglit, 
however,  .still  be  a  n.  vvous  reti-  \  i-  >  mi.'  the  jncal  nerve  struc- 
tures (plexus  of  Aucrbach  i  i-  he  v\.,  ,  of  th.  .stomach.  althouKh 
this  is  not  so  probahlr  a-  „T  t  i.-,  depriid.-i.t  upon  >  cie  clicmicai 
o.xeitation  of  tlie  gland  cells  by  substances  appearintr    u  the  blmxl 


■feas  a  marked 
II         ■■xtract,  or 
■>  <>-    ,,(  ptic  (lines- 
he  main  stomach. 


If' 


64 


PHYSIOLOGY   FOR   DENTAL   STUDENTS. 


jl 
! 


as  a  ivsult  of  iihsorptioii  from  tli.;  stoiuadi.  Tliis  '•honiioiic" 
(st'e  p.  124)  is  not  iiumvIv  absoilK-d  food,  for  no  jrastric  si'cretioii 
occurred  when  solutions  of  meat  extract,  or  of  peptone  were  in- 
.jected  nitraveuously.  It  must  therefore  be  some  substance  that 
IS  absorbed  into  tlie  blood  from  the  mucous  mend)rane  of  the 
stomach,  and  which  is  produced  in  this  as  a  result  of  tlie  action 
of  the  gastric  contents  on  its  cells.  In  confirmation  of  this  view 
it^has  been  .shown  that  boiled  extracts  of  the  mucous  membrane 
of  the  pyloric  region  of  the  stomach  (made  with  water  or  weak 
acid  or  solutions  of  peptone  or  dextrin)  eause  some  gastric  juiee 
to  be  secreted  when  they  are  injected  in  small  quantities  everv 
ten  minutes  into  a  vein,  similar  injections  of  the  extracting  fluids 
themselves  being  without  effect. 

We  are  now  provided  with  the  necessary  facts  upon  which  to 
draw  a  completed  picture  of  th.'  medianism  of  gastric  secetion 
The  satisfaction  of  taking  food  causes  appetite  juice  to  How  and 
this  soon  digests  some  of  the  protein.  The  i)roducts  of  this  diges- 
tion, along  with  the  extractive  substances  of  the  food,  after  some 
time  (which  is  probably  quite  short  in  the  case  of  man),  gain  the 
pylorus,  where  they  act  on  the  mucosa  to  produce  some  hormone 
which  becomes  absorbed  into  the  blood  and  stimulates  further 
secretion  of  the  juice.  As  digestion  proceeds  juice  therefore  con- 
tinues to  be  secreted.  The  appetite  juice  sets  the  process  agoing  • 
It  Ignites  gastric  digestion. 

The  Active  Constituents  of  Gastric  Juice.— When  there  is  no 
fooil  111  the  stomach,  a  certain  amount  of  the  mucous  secretion 
IS  present  in  it,  and  most  of  the  gland  cells  are  filled  with  zymo- 
gen granules  (see  j).  40).  An  extract  (made  with  glvcerine) 
of  the  muco.sa  in  this  resting  condition  exhibits  no  digestive 
powers;  but  if  the  muco.sa  be  first  of  all  macerated  with  weak 
hydrochloric  acid,  the  extract  becomes  highly  active,  because  it 
contains  large  amounts  of  the  proteolytic  ferment  pepsin.  Other 
cells  in  the  stomach  produce  the  necessary  hydrochlork  acid 
It  may  be  concluded  therefore  that  during  the  process  of  secre- 
tion the  zymogen  granules  in  the  cells  are  acted  on  bv  hvdro- 
chloric  acid  and  converted  to  pepsin.  In  conformitv  witii'this 
It  has  been  found  that  the  secretion  of  a  pouch  of  stomach  pre- 


ll: 


DKiESTKtN    IN    Till'.    STOMACH. 


G5 


pnrcd  from  tlio  pyloric  region  pos.s('ssf'S  no  difjcstivp  activity,  for 
in  this  rctrioii  no  hydrochloric  ncid  is  secreted.  The  activation 
of  this  pepsinogen  can  also  be  accoinj)lishe<l  by  tissue  extracts 
and  by  the  products  of  micro-organisnial  growtii.  Because  of 
sucli  growth  in  the  stomach  contents,  it  is  often  found,  in  dis- 
eased conditions  in  which  there  is  no  acid  secretion,  that  active 
l)epsin  is  pn  s<  nt.  Accompanying  tlie  jx'psin,  if  indeed  not  iden- 
tical with  it,  the  ga.sti'ic  juice  contains  the  milk-curdling  ferment, 
r()iinii.  It  also  contains  a  fat-splitting  ferment,  lipasr,  whose 
activities  are,  however,  limited  to  emulsifii  d  fats. 

The  most  remarkable  constituent  of  the  gastric  secretion  is 
InnlrocMofk  acid,  which  in  some  animals,  such  as  the  dog,  may 
attain  a  percentage  of  0.6,  being  usually  about  0.2  in  the  case  of 
man.  It  is  derived  from  the  parietal  cells  of  the  glands  in  the 
cardiac  region  of  the  stomach,  none  being  i)rcsent  in  the  secre- 
Mon  of  the  i)yloric  region,  where  there  are  no  parietal  cells. 

The  source  of  the  acid  is  of  course  the  blood,  for  although  this 
is  practicall.v  neutral,  yet  it  contains,  on  the  one  hand,  substances 
such  as  sodium  bicarbonate  wliicii  readily  yield  hydrogen  ions, 
and  on  the  other,  cidorides  wiucii,  by  dissociation,  make  chlorine 
ions  readily  available.  Although  it  is  thus  possible,  in  the  light 
of  modern  piiysico-chemical  tea  ling,  to  formulate  an  eipiation 
for  the  reaction,  yet  we  ar<'  at  a  loss  to  explain  why  just  at  this 
j)articular  place  (i.  e..  in  the  gland  cells  of  the  stomach)  in  the 
animal  body  and  nowhere  else  tlie  ("1-  and  Il-ions  should  be 
l>icked  out  of  the  blood  and  secreted  as  IICl. 

Little  as  we  know  about  the  cause  and  mechanism  of  the  secre- 
tion of  hydrochloric  acid,  we  do  know  something  regarding  its 
value  and  use  in  the  i)roccss  of  digestion,  and  in  general  we  may 
stat«'  that  this  is  partly  regulatory  and  partly  digestive.  It  is 
rryiihitory  in  tiiat  it  serves  as  the  exciting  cause  of  subse<iuent 
events  in  the  digestive  process,  and  digrstice  not  qidy  in  that  it 
act\ially  a.ssists  in  the  break-down  of  protein,  but  also  because  it 
may  cause  a  certain  amount  of  acid  hyilroiysis  of  sugar  after  it 
has  neutralized  all  the  alkali  of  the  swallowed  saliva.  Its  action 
on  protein  is,  however,  tlie  most  important,  for  it  initiates  pro- 
teolytic  break-down    by    producing   so-called   acid   protein    on 


6G 


I'lrVsIor.oOY    KiiR    DKNTAF,   STIDENT^ 


n 
ff 


M 


which  thf  pepsin— itsflf  also  tlcpciulciit.  as  we  have  s.'eii.  on  a 
I)r('liniiiiary  activation  hy  acid— th.n  unfohls  its  action.     Ah  the 
I)rotcin   becomes  i»i'oj;rcssivcly   broken  down   into  i»roteos'-  and 
peptones,  the  acid  l)econies  more  and  more  al)sorbed.  so  tliat  it  is 
some  consideraWe  time  after  jrastric  difjestion  lias  started  before 
any  acid  is  allowed  to  exist  in  tlir  free  state.     It  is  only  after 
some  of  it  is  free  that  it  can  hydrolyse  sngrnrs  or  perform  an- 
other important  function,  namely,  ad  as  an  (iiilis< ptic.     In  this 
regard,  liowever,  it  must  be  remend)ere(i  that  it  is  only  towards 
certain  organisms  that  .such  antiseptic  action  is  displayed,  for 
there  may  be  bacteria  in  the  gastric  contents  even  in  cases  of  ex- 
cessive .secretion  of  hydrochloric  acid.    The  undmibted  tendency 
for  intestinal  putrefaction  to  increase  when  there  is  a  deficient 
secretion  of  hydrocidoric  acid  is  probably  dej)endent  more  upon 
the  delay  in  dig<-stion  which  this  occasions,  than  upon  any  spe- 
cific antiseptic  power  of  hydrocidoric  acid.     During  the  time  that 
elapses  before  a  sutticiency  of  hydrochloric  .  -u]  has  accumulated 
to  i)erform  this  function,  bacterial    fii  iiici.  .;tion  occurs  in  the 
stomach  contents.     Carbohydrates  are  broken  down  by  this  i)ro- 
ces.s,  at  first  into  simj)le  sugars  and  then  into  lactic  acid,  which 
may  come  to  be  present  in  consideraiile  amount  before  the  fer- 
mentation  i)rocess   is   terminat<'d.      For   th.-se   reasons  we   find 
that  there  is  relatacly  much  more  lactic  acid  detectable  in  the 
ga.stric  contents  removed  by  the  stomach  tube  at  an  early  stage 
ill  ga.stric  digestion  than  later. 

The  .so-called  acid  albumin  which  results  from  the  action  of 
the  acid,  becomes  attacked  by  the  jM-psin.  which  still  further 
breaks  it  down  into  so-called  i)roteose  and  pei)tones,  which  do 
not  coagulate  by  heat  and  which  become  progressively  more  dif- 
fusible through  animal  membranes.  Although  pep.sin  is  capable 
of  carrying  the  digestive  jtrocess  far  beyond  the  stage  of  pej)- 
toncs.  this  does  not  occur  in  the  comi)aratively  short  time  (about 
six  hours)  during  which  the  fimd  remains  in  the  stomach.  Slight 
as  is  this  action  of  pepsin  in  the  .stomach,  it  nevertheles.s  appears 
to  be  of  considerable  importance  for  the  subseciueiit  digestion  of 
protein  by  the  other  i)roteolytic  feriuent.s,  trypsin  and  erepsin 
(see  p.  7.')),  wiiich  operate  in  the  small  intestine.    Thus,  a  given 


UIOKSTION    IN    Till-:    ST(l.\'  \*'II. 


fi7 


aiiiouiit  of  1)1(M)(1  scriiin  Ik-ooiih's  dijrcstcd  imicli  I'urtlu'f  in  ii 
tlivf'ii  time  l)y  a  srivcii  anuniiit  ol'  tr\  i)sin  if  it  ifccivi-s  a  i)rfiiin- 
inary  (iifrcstidii  by  inraiis  of  jx'itsiii.  than  when  il  is  actr.l  on  l>y 
trypsin  alone,  and  crcpsin  will  cause  no  dijiestioii  at  all  unless 
the  native  protein  is  first  of  all  aeted  om  either  by  pepsin  or 
trypsin.  lint  peptic  digestion  is  not  essenltal  for  life,  for  sev- 
eral cases  are  now  on  record  in  which  individuals  liave  thrived 
after  the  stomach  has  been  removed. 

The  milk  curdling  action  of  gastric  juice  is  due  partly  to  the 
Vydroehloric  acid  and  partly  to  pepsin.  Curiously  enough  the 
curdled  milk  underg(H>s  little  further  change  until  the  food  has 
got  to  tlic  small  intestine. 

The  lipa.se  in  gastric  juice  can  act  oidy  on  emulsified  fat  and 
in  neutral  or  alkaline  reaction.  Fat  digestion  cannot  therefoi'c 
be  an  important  gastric  process. 

It  has  been  supi)osed  that  there  is  a  certain  specific  adaptation 
between  the  chemical  nature  of  the  food  and  the  amount  and 
strength   of  the   gastric   sei-retion.      For   exami)le,    it   has   been 
found,  by  observations  on  the  juice  flowing  from  a  miniature 
stomach,  that  feeding  in  the  ordinary  way  with  bread  causes  a 
maximal  secretion  during  the  fir.st  hour,  whereas  with  an  eipiiva- 
lent  amount  of  flesh  the  maximum  occurs  during  the  first  and 
„ ,  >  si  hours,  and  with  milk  it  is  delayed  till  the  third  or  fourth. 
■  :  pi   teolytic  i)0wer  the  bread  juice  is  much  the  strongest  of  the 
ti.     -,  but  it  contains  a  lower  i)ercentage  of  acid  than  the  others. 
The  Movements   of  the   Stomach.— Solid  food  after  being 
swalloweil  accumulates  in  the  body  of  the  stonuich,  where  on  ac- 
count of  an  absence  of  movements  it  is  not  uniformly  acted  on 
by  the  gastric  juice,  its  outer  layers  only  becoming  digested.     In 
the  case  of  the  man,  however,  some  of  the  food,  because  of  its 
semi-fluid  nature,  i)as.ses  beyond  the  so-called  transverse  band 
and  into  the  pyloric  region,  in  which  waves  of  contraction  nnike 
their  appearance.     Starting  very   faintly   at   this   point,   these 
waves  travel  towards  the  pylorus  and  become  gradually  more 
marked  until  they  may  become  so  ileep  as  practically  to  cut  olT  a 
portion  of  the  pyloric  region  from  the  rest  of  the  stomach.    This 
last  portion  of  the  pylorus,  sometimes  culled  the  pyloric  canal, 


Jii 


m 


PIIYSI0IX10Y    FOR   DEXTAL   STUDENTS. 


gradually  contrafts  on  the  food  which  has  been  foreed  into  it, 
thus  tending  to  ejeet  it  through  the  pvlorie  sphincter,  or,  if  this 
is  elo.sed,  to  cause  it  to  pass  back  again  as  an  axial  stream  int<i 
the  proximal  part  of  the  pylorus,  which  luis  been  called  the 
nijloric  rc.stibiilf  (wm-  Fig.  5).  These  waves  occur  every  fifteen 
to  twenty  .seconds,  three  or  four  being  present  in  the  pyloric 
vestibule  at  the  same  time.  They  become  more  marked  as  diges- 
tion proceds,  and  are  accompanied  by  a  gradual  diminution  in 
size  of  the  body  of  the  stomach.  Their  function,  besides  carrying 
the  food  towards  the  outlet  of  the  stomach,  is  to  keep  it  properly 
mixed  with  the  gastric  juice. 

The  Opening  of  the  Pyloric  Sphincter,— The  mere  pressure 
with  which  the  contents  of  the  vestibule  are  thus  driven,  witli 
each  peristaltic  wave,  against  the  pyloric  sphincter  does  not, 
however,  in  itself  serve  to  open  it ;  for  half  an  hour  after  feed- 
ing with  protein,  for  e.\aini>le,  no  food  may  i)ass  the  sphincter, 
although  during  this  time  there  may  have  been  well  over  a  hun 
dred  peristaltic  waves.  Nor  is  it  the  con.sistency  of  the  food 
which  controls  the  oi>e!iing.  It  must  therefore  be  some  chemical 
pr.>perty  which  the  food  aci|uii-es  during  its  stay  in  the  stomach. 
This  has  definitely  been  shown  by  Cannon  to  be  the  presence  of 
free  acid.  By  measuring  the  length  of  the  skiagram  shadow  in 
the  intestines  after  feeding  cats  with  bisnnith-impregnated  foods 
rendered  acid  or  alkaline,  it  could  be  clearly  shown  that  acid 
liastened  the  initial  discharge,  whereas  alkalies  retarded  it,  and 
observations  through  a  fistula  in  the  vestibule  showed  that  any 
delay  in  the  appearance  of  acid  in  the  contents  was  associated 
with  a  delay  in  the  opening  of  the  sphincter.  liut  the  sphincter 
does  not  remain  open ;  it  (juickly  close.'?  after  a  little  ehym(>,  as 
the  half  <ligested  food  is  called,  has  got  through  it.  This  <'los- 
ure  is  due  to  the  free  acid  acting  on  the  duodenum,  where  it 
stimulates  afferent  nerve  endings  that  cause  the  sphincter  to 
close  and  to  keep  closed  so  long  as  any  acid  remains  in  the  duo- 
denum. Whenever -this  acidity  has  become  neutralized  by  the 
alkali  present  in  the  bile  and  pancreatic  .iuice,  the  acid  on  the 
stomach  side  again  becomes  operative  and  the  .sphincter  oi)ens. 
We  must  conclude  that  the  pyloric  sphincter  is  under  the  eon- 


DIGESTION   IN   THE   STOMACH. 


69 


trol  of  a  nerve  center  which  transmits  influences  that  tend  to  re- 
lax the  sphincter  when  tlie  afferent  tihers  runniiifr  to  it  from  tiie 
stomach  sich-  are  excited  by  acid,  but  whidi  cause  it  still  more 
powerfully  to  contract  when  the  acid  acts  on  afferent  libers  hav- 
ing their  terminations  in  the  duodenum.  When  both  afferent 
l)atlis  are  simultaneously  stimulated,  the  duodenal  j)redominates 
over  the  gastric,  so  that  the  sphincter  remains  closed  until  the 
acidity  of  the  chy;.ie  in  the  duodenum  has  all  been  neutral i/e<l, 
and  this  seems  to  be  true  however  faint  the  acidity  may  be  on 
the  duodenal  side  and  however  strong  on  the  stomach  si<le.  The 
reflex  arc  is  situated  in  the  walls  of  the  pyloric  region  and  duo- 
denum, for  it  operates  after  complete  isolation  from  the  central 
nervous  system.  It  is  a  function  of  the  plexus  found  present  in 
the  walls — the  myenteric  plexus. 

Rate  of  Discharge  of  Food  from  the  Stomach.— The  acidity 
of  the  ga.stric  contents,  as  we  have  .just  seen,  must  attain  a  cer- 
tain d(gree  before  it  becomes  an  ade>|uate  stimulus  for  the  oi)en- 
ing  of  the  pyloric  sphincter,  and  consequently  the  rate  at  which 
the  different  food  stuffs  leave  the  stomach  is  to  a  large  extent 
jiroportional  to  their  power  of  combination  with  the  acid.  Pro- 
teins, combine  with  large  amounts  of  acid,  so  that  their  initial 
discharge  is  delayed  and  their  subse(|uent  i)assage  slow.  Car- 
bohydrates absorb  but  little  acid,  so  that  they  begin  to  leave  early 
and  the  stomach  is  soon  emptied  of  them.  The  pa.ssage  of  fats  is 
peculiar;  when  taken  alone,  which,  however,  is  scarcel.v  ever  the 
ca.se,  they  seem  to  bring  about  a  partial  relaxation  of  the  pyloric 
sphincter,  so  that  bile  and  pancreatic  juice  regurgitate  into  the 
.stonmch  and  some  fat  may  pa.ss  out,  but  the  subse(|uent  dis- 
charge into  the  intestines  is  ver.v  slow,  so  slow  indeed  that  each 
discharged  portion  seems  to  become  completel.v  absorbed  before 
any  further  discharge  occurs.  When  fats  are  mixed  with  other 
foods,  the.v  materially  delay  the  discharge.  These  effects  are 
no  doubt  due  in  part  to  the  inhibitor.v  influei'"e  which  fats  have 
on  gastric  secretion;  and  in  j>art  to  the  liberatioii  of  fatty  acid  in 
the  duodenum  by  the  action  of  pancreatic  lipase.  This  fatty  acid 
seems  to  be  liberated  more  <iuickly  than  it  becomes  neutralized 
by  alkali. 


m  \ 


70 


IMIYf>IOLCXJy   FOK   DKNTAL   STUDKXTS. 


Wjitcr  aloiio  begins  to  It-avo  the  stomach  almost  iinnu'diatt'ly 
after  it  is  taken,  beeause  tlie  sphincter  opens  before  an  acid 
reaction  has  been  acquired,  and  remains  open  on  account  of 
there  being  no  acid  in  the  duo(h'num  to  effect  its  closure.  Water 
stays  for  too  sliort  a  time  in  the  stomach  to  excite  any  gastric 
s<'cretion,  and  conseipiently  it  readily  carries  infection  into  the 
intestine.  The  discliarge  of  raw  egg  albumin  is  peculiar.  Like 
water  it  Ijcgins  to  i)a.ss  the  j)ylorus  immediately  after  ingestion, 
its  reaction  for  some  time  being  alkaline;  it  becomes  acid  later, 
.so  that  the  discharge  becomes  int«'rmittent  because  of  the  duo- 
denal reflex.  The  consistency  of  food  itself  does  not  affect  the 
rate  of  discharg.^  niiless  hard  jiarticles  are  present  in  it,  when  a 
marked  retardation  occurs. 

It  is  well  known  that  the  gastric  contents  are  but  .slowly  dis- 
charged into  the  duodenum  when  there  is  excessive  gas  accu- 
mulation. This  is  due  to  the  atony  of  tile  .stomach  which  accom- 
panies pathological  gas  accumulation. 


CHAPTER  VII. 

DKiKSTION   (Coufil). 

Intestinal  Digestion:   The  Movements  of  the  Intestines: 

Absorption. 

The  Secretion  of  Bile  and  Pancreatic  Juice.— Hcsidt's  eaus 
iiig  ivflt'x  closurt'  of  the  pyloric  spliiiictfr,  the  coiitiu-t  of  tht- 
chiftue,  whif'h  is  the  iiaiiu-  jiivt-ii  to  tlif  sfiui-difrfstcd  food  as  it 
leaves  the  stomaeli.  witli  the  diioih'iial   mucosa  inaugurates  the 
l)rocesses  of  intestinal  digestion  by  exciting  tiie  secretion  of  bile 
and  pancreatic  juice.     Neither  of  tiiese  juices  is  secreted  into  the 
intestine  (hiring  fasting;  l»ut  both  begin  to  How  very  soon  after 
taking  food,  and  they  gradually  increase  in  anunmt  for  about 
three  hours,  and  then  rapidly  decline.     The  bile  at  Hrst  conies 
mainly  from  the  gall  bladder,  in  which  it  has  accumulated  dur- 
ing fasting.    When  the  gall  bladder  sup|ily  is  exhausted,  the  bile 
comes  directly  from  the  liver  without  entering  the  gall  bladder, 
and  this  secretion  becomes  more  and  more  marketl  as  digestion 
proceeds.     The  storage  of  bile  which  occurs  during  fasting  is 
necessitat.'d  by  the  fact  tliat  although  it  is  not  re.|uin'd  in  the 
intestine,  bile  is  nevertheless  being  constantly  ]iroduced  by  the 
liver,  because  it  is  an  excretory  produe     as  well  as  a  digestive 
fluid.     It  must,  therefore.  Ih-  got  rid  of  from  the  blood,  but.  !)«•- 
ing  also  useful  for  dige.stion.  it  is  stored  until  it  is  reciuired  to 
a.ssist  in  this  process. 

The  sudden  discharge  of  iiile  from  the  gall  bladder  is  depen- 
dent upon  a  nerve  reflex  .'Xciled  by  tiie  contact  of  the  acid  clivme 
with  the  duodenum.  The  increa^'d  secretion  of  bile  from  the 
liver,  like  th<'  secretion  of  pancreatic  juice,  is  however,  inde- 
pendent of  nerves,  for  it  has  been  fountl  that  the  application  of 
weak  hydrochloric  acid  to  tlie  duodenum  causes  the  juices  to  flow 
after  all  the  nerves,  but  not  the  blood  vessels  of  the  duodeiinm 
have  been  cut.  The  only  way  by  which  such  a  result  can  be  ex- 
plained is  by  assuming  that  the  acid  causes  some  chemical  sub- 

71 


l'IIYSIOI,(MiY    FDU    DKNT.Xr,    tJTfDKNTS. 


stance  to  I)f  iiddfd  to  tlu-  blood,  whidi  tlicn  carrit's  it  to  tlic  i)aii- 
crcas  and  liver,  ui)on  the  cells  of  which  it  exercises  a  stinmlatinj,' 
influence.  That  this  is  the  correct  explanation  was  shown  by 
studyinjf  the  effect  which  is  pnxluced  on  the  secretion  of  i)an- 
creatic  juice  and  bile  by  intravenous  injections  of  decoctions  of 
intestinal  mucosa  made  witii  weak  acid  and  subse(|uently  neu- 
tralized. An  immediate  secretion  resulted.  The  acid  extract  evi- 
dently contained  so hormone  whose  production,  in  the  normal 

process  of  digestion,  is  evidently  occasioned  by  the  contact  of  the 
acid  chyme  with  th-  duodenal  mucosa.  This  hormone  is  called 
sivrdin  but  we  know  very  little  of  its  e.vact  chemical  nature.  It 
is  not  a  ferment,  for  it  withstands  heat:  it  is  not  a  protein,  for  it 
can  be  extracted  by  lioilintr  the  mucous  memb?-ane  with  weak 
acids  after  tr.-atment  with  alcohol.  It  is  readily  oxidized  in  the 
l»resenci'  of  alkalies,  and  is  of  the  .same  nature  in  ;  11  animals. 
It  is  useless  to  jfive  .secretin  as  a  druf?  with  the  hope  that  it  will 
stinuilate  i)ancre;itic  secretion,  for  it  is  not  absorbed  from  the 
lumen  of  the  intestine. 

Although  most  abundant  in  the  muosa  of  the  duodenum  and 
jejunum,  secretin  is  also  present  in  the  mucosa  of  the  lower  end 
of  the  small,  an<l  to  a  lesser  degree,  in  that  of  the  large  intcsi'ie. 
Soap  solutions  act  like  acid  in  pi-oducing  secretin.  A  fatty  n  ,  '. 
therefore,  excites  the  flow  of  much  j)ancreatic  juice  and  bile,  i 
cause  the  fatty  ,  cid  which  is  si)lit  off  unites  v.ith  alkali  and 
forms  soap. 

It  may  be  that  the  very  first  portion  of  pancreatic  juice  to  be 
.secreted  after  a  meal  is  Miken.  is  due.  not  to  secretin  formation, 
but  to  reflex  nervous  stinuilation  of  the  i)ancreas.  In  comparison 
with  the  hormone  control  the  nervous  control  is.  however,  (piite 
unimportant  in  pancreatic  .secretion,  for  there  is  no  necessity  in 

the  intestine,  as  in  the  mouth,  or  to  a  less  degi in  the  stomach. 

for  a  <|uick  response  to  the  stimulus  produced  by  the  presence 

of  food.     The  histological  changes  produ 1  in  the  gland  cells  of 

the  i)ancreas  by  secretory  activity  are  much  the  same  as  in  the 
parotid  glan<ls. 

Functions  of  the  Bile  and  Pancreatic  Juice.— These  two 
juices  are  very  closely  associated  in  their  activities.     This  fact 


INTKSTINAI-  DUil'.STION . 


7:j 


is  pt'i-haim  imist  strikingly  tit  inonstratctl  in  tlic  (li>rfstit)ii  aiitl  iib- 
sorptiiiii  of  fat;   for.   in   the  altsi-ncf  of  citluT  stcrftion.   larui- 
aniouiits  of  unal)st)rlu'<l   fat  apju-ar  in  tin-  tVffs.      Moth  juicfs 
contain  relatively  lar^e  amounts  i)f  nlhili,  uhirh  iinitnili:<s  tin 
itciditii  of  ihr  chjiuic.    In  tlie  i)anereatie  .juice  alone,  for  example. 
th»'rt>  is  a  sulficient  concentration  of  sodium  cailnmate     to  neu- 
tralize the  acid  in  an  ei|ual  vulume  of  gastric  juice.     The  action 
of  pepsin  disapjiears  whenevei-  the  chyme  becomes  alkaline  aiitl 
eonditioiis  thus  become  suitable   for  the  activities  of  the   i)an- 
ereatic  enzymes.     Hesides  its  neutrali/iuK  action,  tlie  bile  causes 
the  chyme  to  assume  a  somewhat  jjrcater  consisteiiey.  by   pre- 
eipitntinn  incojnpletely   ])eptt)ni/etl   protein,  as  well   as  pejjsin. 
The  j)rccipitate  becomes  rcdissolveii  when  excess  of  bile  has  be- 
come mi.\ed  with  it.  and  the  sifrniticance  of  the  precipitation  may 
be  that  it  causes  a  temporary  delay  in  thi'  movement  of  the  cliyme 
along  the  d\ioilenum.  thus  allowin<r  it  tt)  Itecome  proi>erly  mixetl 
with  jtancreatic  juice  before  it   moves  furth-r  along  tiie  intes- 


tine 


Composition,  Properties  and  Functions  of  the  Bile.— 

Water ^^-i' 

Total  St>litls l-ll 

of  which  : 


( )rg'aiiic  ■< 


I'.ih'  Salts !».U 

Lecithin  ami  ("hole.sterol 1.10 

Mucitioitl   Sid)stance     ) 
Pigment  ) 


Inorganic   Salts 


D.TS 


The  bile  is  a  grcenisli-yellow  tluitl  of  sticky  consistency  antl 
bitter  taste.  Its  most  interesting  constituents  arc  the  bile  salts. 
which  are  complex  organic  substances,  having  an  important  func- 
tion to  perform  in  as.sisting  the  lipas"  and  amyloi)sin  of  pan- 
creatic juice  in  their  digestive  activities.  (tt}«*rwise  the  bile  con- 
tains no  digestive  enzymes.  The  cholesterol  is  not  a  readily 
soluble  substance,  so  that  i'  is  apt  to  become  i)reciiiitated  in  the 


74 


I 


PIIY.sIUUKJV   FOB   DKNTAL   STUDENTS. 


I)il.'  <lu«-t  aiirl  piiuw  ,f„U  sioti,s.  Thf  <list.-iitioii  of  tli.-  .liicts 
whit'li  these  |ti(Mlii('<'  may  .•aim.'  ymit  pain  (biliary  colic).  Tlic 
formation  of  pall  stones  is  cncoiirap-.l  by  iiiflanniiatorv  processes 
of  the  n.ueons  n»'iiiJ)raMe  of  the  .hiets.  When  bile  fails  to  reach 
the  intestine,  because  of  blocking?  the  <lncts.  either  by  >;i,il  stones 
or  by  inflaniiiiatory  sw-.-llin^  of  tlu-  mucous  membrane,  the  <li- 
Kestion.  especially  of  fats,  is  much  interfered  with,  and  the  fa-ces 
become  foul  snu-llin};  and  pale  in  color. 

The  Composition  and  Properties  of  Pancreatic  Juice.— The 
pancreatic  .juice  contains  three  important  enzymes:  Upas,    (act- 
fc^  |r»«4,^"*^'  on   fats).  iimiiJopsii,    (actiuK  on  starch),  and   tnfpsi>,o,/t  u 
I  ^^\f^j,    .'"''*>«  •»"  P'-oteiu).     Although  the  bile  contains  no  enzymes,  it 
T^  IS.  as  we  have  seen,  a  most  imj.ortant  accelerator  of  the  activities 

of  the  lij.ase  and  amylopsin  of  the  pancreatic  .juice.     Bib-  has  no 
action  on  trypsinog..n.  which  is  nevertheless  without  any  action 
until  it  has  become  changed  into  trDpsin.     This  does  not  occur 
until  the  pancreatic  .juic-  has  i-eached  the   intestine,  when  the 
activation  is  brou>?ht  about  by  a  fennent  j)resent  in  the  intes- 
tinal .juice   (.secretion  of  I.ieberkiihn's  follicles),  called  cnliro- 
liiiasf.     The  int.-stinal  .juice  contains  this  activator  only  when 
it  is  re<iuired :  it  is  absent,  for  e.xample.  in  the  .juice  that  is  se- 
creted as  a  result  of  mechanical  stimulation  of  the  intestinal  mu- 
cosa, but  it  inuiiediately  aj)i)ears  when  some  pancreatic  secretion 
is  applied  to  the  nuicosa.     Knterokinase  is  not  the  only  substance 
which  can  activate  tiyj.sinoifen.  for  the  a.ldition  of  calcium  salts, 
tiie  coiifact  of  the  .juice  with  leucocytes,  as  in  sranulation  tissue, 
and  even  mere  standinpr  of  tli.'  .juice,  have  a  similar  etfect.    If  the 
l.juicreatic  juice  in  esr  ipiufr  from  the  duct  should  run  over  gran- 
uli.tion  tissue,  as  occurs  wh.-n  ;i  fistula  of  the  duct  is  made,  it  be- 
comes activated  and  unless  precautions  ..n-  taken  it  will  excoriate 
the  wound.     Shoidd  it  escape  into  th.'  peritoneum,  as  when  a 
cyst  bursts,  it  also  becomes  activated.     Uy  bein^r  secreted  in  an 
inactive  .state,  the  proteolytic  enzyme  .t..vc|()|,<  no  ,|ijj,..stivc  ac- 
tion on  the  i)ancreatic  duets. 

It  will  be  renuMubered  that  the  amount  oi  jrasti  i.-  juice  secreted 
varies  with  different  foods,  beini.'  relatively  more  abu!!<iant  nn  a 
diet  of  bread  than  on  one  of  milk,  or  even  meat  ([).  (i:{).     8iini- 


INTESTINAI-  imiKSTION. 


75 


lar  .|uaiititativ.'  <liff.Mvii.-os  oxist  in  th.'  s.rn'ti.Mi  of  piiiu'iriiti.- 
juic."  Hii.l  this  is  pn)l)ahly  t.)  »«•  .'xplaiii.'.!  I>y  tli.-  varying  .|iiaiiti- 
tifs  ..f  aci.l  cliym.'  .•<.min«  in  conta.-t  with  th.'  .lu.ul.'nal  imn'osa. 
Chemical  Changes  Produced  by  Intestinal  Digestion.— In  the 
lou'fr  portion  of  th<  duothinim  <ni<l  in  thr  jijiiinnn.  Ih<  'lincslivr 
,>n>imfs  of  Ih,  pinirr, alir  jiiia  mi  on  th,  food  in  fnll  intrnsitif. 
Th.'  trypsin  rapi.Uy  hy,lf..iyz»"s  th."  prot.'ins  to  p.-pton.'.  whii-h  if 
it  is  not  inimediatciy  ahsoih.-.l  may  h.'c(nn.'  tnrtli.'i-  brok.'ii  .lown 
to  amino  bo<li.'s  i.n.i  ai'omati.-  .'omiM'im.ls.    The  lipas.-  hy.lrolys.-s 
fat  to  jflvc-i'i-iiu'  an.l  fatty  a.i.l.  which  ar.-  absorbf.1.  th.-  f..rm«'r 
as  such,  the  bitt.-r.  nft.-r  combining  with  alkali  to  form  soap.  or. 
if  no  alkali  be  available,  with  bih-  salts  to  form  compoun.ls  which 
like  the  soap  an-  sohibl.'  in  wat.-r.    Amyi.ipsin  conv.-rts  into  mal- 
tose any  starch  or  .lextrines  which  the  ptyalin  of  saliva  has  failed 
to  act  on.    The  maltos.'  thus  form.-.l.  an.l  the  oth.-r  .iisaccharides. 
can.'  sugar  and  lactos.'.  altlDUgh  solui)!.'  in  wat.-r.  do  not  become 
absorlM'd  into  the  bloo.i  as  such  but  b.'com.'  further  liy.lrolyzed 
by  th.'  action  of  so-call.'.l  iiiv.-rting  .'nzymes,  of  which  there  is  one 
t-;,,'  .'a.'h  disa.-cluu-id.'  (s.'.-  p.  'i.V,.    Th.'s.-  inverting  .'uzymes  an- 
more  pl.'Utiful  in  extracts  of  th.-  mucosa  than  in  tlu'  int.'stuial 
juice  its.-lf.  from  whi.-h  w.-  conchi.le  that  it  is  oidy  aft.-r  they 
have  been  absorbed  int.)  th.-  c-lls  of  th.-  intestin.'s  that  th.'  uisac- 
.-harides  an-  invert.-.!.     Th.-  i)roe.-ss.  in  other  words,  is  an  in- 
tracellular one. 

One  other  enzyme  .-xists  in  the  intestinal  juice.  nam.-ly.( /v/mi". 
It  acts  on  partially  liy.lrolyz.-.l  prot.-ins  an.l  on  cascinogen,  so 
as  to  hydrolyz.'  th.-m  compl.-t.'ly  into  tiie  amino  compoun.ls. 
Krepsinis  a  wi.lely  distribut.-.l  .-nzym.'  in  th.'  animal  b.).ly.  be- 
ing present  in  practically  ev.-ry  tissu.'.  although  it  is  abs.-.it  from 
blood  plasma.  It  is  present  in  much  gn-ater  conc.-ntrati.>n  in  .'X- 
traets  of  the  intestinal  muc.isa  than  in  suc.-us  enterieus,  so  that, 
like  the  inverting  enzym.'s.  it  possibly  .lisplays  its  action  while 
the  protein  is  b.'ing  ab.sorbed  as  proteoses  an.l  peptont>s.  It  s.'rves 
as  the  last  barri.-r  again.st  the  entry  into  the  bloo.l  of  prot.-in  in 
any  other  form  than  as  a  mixture  of  amino  bodies.  Less  om- 
pletely  digested  i.roteiu  is  poisonous  wli.-n  added  to  tlie  bl.K).l 
(p.  152). 


70 


l'liy.sI«i|,<KiY    K(»B   DINTAI,   STt'DKNTS. 


, 


M(wt  of  th.'  tVxHl  \h  now  in  a  Nuitahh"  fomlition  for  absorption. 
|{.'for.-  wo  |»ro,.,.,.,l  f„  Ntu.ly  tin-  nafniv  of  this  pron-ss  liowrvi-r 
lh.>ri>  are  on.'  or  two  furth.-r  digentiv.-  changeM  that  wr  nmst  con- 
tiiilcr. 

The  Digestive  Function  of  Intestinal  Bacteria.-()n  acci.unt 
ot  the  antiM.ptic  action  of  fi.  hv.lro.'hh)ric  a.'i.l.  th.-n-  is.  onli- 
iiiinly.  no  baftorial  jrrowth  in  th.>  stomach,  but  th.-  n.-utrali/.a- 
tion  of  aci<l  by  pancrnatic  jui(v  and  bile  in  the  intestine  pro- 
vides a  perfeet  nie.jinii.  i  -r  sue!,  growth.  The  extent  i-n<l  nature 
of  the  baeterial  growth  varies  very  greatlv  aeeordin^  to  the  na- 
ture of  the  diet. 

There  ean  be  no  doubt  that  the  niiero-organisnis  ar.-  a  valuable 
aid  to  digestion  in  the  ease  of  most  animals,  espeeiallv  of  those 
whom,  diet  ineludes  e.-lhilose.     Indeed,  in  sueli  animals  as  tl.<. 
herbivora  si>eeial  provision  is  made  to  eneourage  baeterial  growth 
by  the  greiit  length  of  the  large  intestine,  for  without  baet.M-ia, 
digestion  of  <-ellu!ose  is  impossible.    Thus  if  n.-wly-halehed  ehieks 
Iw  fed  with  .sterilized  jtraiii  they  sueeiinib  in  about  two  we.-ks. 
but  if  a  small  amount  of  the  exeivinent  of  the  fowl  be  mixe.l 
with  the  grain,  they  thrive,  as  ordinarily.    On  the  ..ther  hand,  if 
th<'  foml  contains  no  cellulose,  animals  may  .levelo|)  and  grow 
with  sterile  intestinal  contents;  thus  guinea  j.igs  have  been  re- 
moved from  th>-  uterus  under  a.sej.tic  conditions  and  kept  in  a 
sterile  i)lace  on  sterilize.l  milk  and  have  thrive.l  and  grown  as 
normal  guinea  pigs.    The  organisms  in  the  intestine  of  man  are 
probably  much  more  useful  than  harmful.     No  doubt  they  are 
parasites,  but  tliey  are  u.seful  (>arasites:  th.-y  work  for  th.-iV  liv- 
ing, not  only  by  assisting  when  necessary  in  th.-  digestion  of 
food  but  also  by  destroying  certain  substances  which,  if  absorlx-d 
would  have  a  toxic  action  on  the  hcst.     Thus  cholin.  a  substanet" 
produced  by  the  digestion  of  lecithin,  is  distinctiv  poi.sonous  but 
It  really  never  gets  into  the  blocnl  becau.se  the  bacteria  d.-stroy  it. 
In  the  ca.se  of  man  bacterial  digestion  occure  both  in  the  small 
and  large  intestines,  and  there  are  varieties  of  bacteria  capable 
of  acting,,,,  all  the  food  stuffs.     They  may  break  up  th.'  sugars 
into  lactic  acid  or  evn  further  so  as  to  form  CO.,  and  II     Ii  has 
been  claimed  that  this  formation  of  lactic  acid  in  the  intestine  is 


INTF^TINAI.  PKlKSTIiiS. 


t  t 


of  bonofit  to  tho  health  of  man  brcnuso  wlu-ii  it  ooo\irs  other  bar- 
trria  which  arc  nion-  haniifiil  than  usofiil  hfconic  (IcHtroycd,  To 
cncouniKc  this  growth  of  lactic  acid  bacteria,  it  has  b.(  ii  rcconi- 
nicnih'il  that  larjrc  (|uantitics  of  sour  milk  slioubl  be  taken.  It  is 
untloubtedly  true  that  sucli  treatment  is  of  benefit  in  numy  per 
sons  who  fiuffer  from  excessive  intestinal  putrefaction,  but  thai 
Rucli  treatment  shouhl  jirolouK  the  life  of  otherwise  healthy  indi- 
viduals is  visionary.  Ah  in  lu-rbivora.  there  are  also  bacteria  in 
man  which  break  up  cellulose,  pro«lucinj?  methane  and  ("().,.  After 
d,  ts  eontainin»  much  v  i,Me  matter,  therefore.  «  lame 
anu.int  of  gas  is  likely  tc  tu'i  lin*"  in  the  intestines.  From 
fats,  the  intestinal  bactenu  juedie-.  .iwer  fatty  acitls,  which 
teiul  to  cause  the  contents  in  ii  •  1' -A.r  jmrtion  of  the  small  in- 
testines to  become  acid  in  i    ■  r-nri 

Although  capable  of  bydrolyzintt  native  protein  from  the  very 
start,  bacteria  act  more  readily  on  protein  that  has  been  partially 
digested  by  the  proteolytic  enzymes  of  tiie  stomacii  and  intes- 
tines.  The  pnxhicts  of  this  action  are  more  or  less  characteristic 
becaus*'  of  the  peciUiar  manner  in  which  the  aromatic  groui)s  of 
the  i»ri)tein  molecule  are  attacked,  producing  from  it  such  sub- 
stance- as  phenol,  skatol,  indol,  etc.,  to  which  the  characteristic 
odor  ()!  the  fa-ces  is  due.   When  protein  has  been  adeciuately  .U- 
gt-sted  in  the  stomach,  it  is  so  rai)idly  acted  on  by  the  trypsin 
(and  erepsin")  of  the  small  gut  and  is  so  quickly  absorbed  that 
bacteria  have  mo  chance  to  act  on  it.    When  protein  has  been  in- 
adeiiuately  digested  in  the  stomach,  however,  the  trypsin  fails  to 
digest  it  (|uickly  enough,  so  that   bacterial    putrefaction  sets  in 
which  may  be  quite  marke  •  in  the  small  intestine,  although  much 
more  so  in  the  colon.    Even  when  they  do  not  find  a  suitable  sub- 
strat  in  the  food,  the  bacteria  attack  the  proteins  of  the  intes- 
tinal .secretions  them.selves,  which  accounts  for  the  well-known 
occurrence  of  this  process  during  starvation. 

The  Immunity  of  the  N&Oa  of  the  Digestive  Organs  Toward 
the  Enzymes  Which  Act  within  Them.— The  immunity  of  tiie 
mucosa  of  the  stomach  and  intestines  seems  to  be  due  in  main  to 
the  presence  in  the  cells  of  the  mucosa  of  anti-enzymes,  that  is  of 
substances  which  can  inhibit  the  action  of  the  various  enzymes 


78 


PIIYSIOI/WY   FOR   DENTAI,   STUDENTS. 


(aiitipopsin,  antitrypsin,  etc.).  As  w.-  should  pxpeet.  very  strong 
anti-enzymes  can  h.-  prepared  from  tapeworms  and  otiier  intes- 
tinal worms.  It  is  in  virtue  of  posst-ssing  tliese,  that  the  worms 
are  r  t  digested.  The  immunity  of  the  gland  eells  and  duets,  as 
qf  the  panereas,  to  the  proteolytic  enzymes  whieli  th<>y  produee 
is  possibly  to  be  e.xi)lained  in  another  way,  namely,  by  tlie  ex- 
istence of  the  enzyme  as  an  inactive  i)recursor  (e.  g.,  trypsino- 
gen)  until  after  the  secretion  has  bwn  carried  to  a  regioii  whose 
walls  contain  the  specific  anti-body.  A  certain  degree  of  im- 
nninity  to  a  possible  destructive  action  of  the  intestinal  bacteria 
may  be  conferred  by  the  nnicin.  whicli  is  quite  abundant,  at  least 
in  the  empty  stomacii  and  in  the  large  intestine.  The  relatively 
poor  growth  of  bacteria  which  occurs  on  inoculating  fiecial  mat- 
ter in  culture  media— although  many  bacteria  can  be  seen  by 
microscopic  examination  to  be  j)resent— is  probably  to  be  ex- 
plained by  their  having  been  killed  by  the  nuicin. 

The  Movements  of  the  Intestines. 

The  luovfmnils  of  the  suiall  inlrstiiH  have  two  functions:  (1) 
to  macerate  and  mix  u])  the  food  and   (2)  to  move  it  along  to- 
wards the  lower  end  of  the  gut.     These  two  functions  are  sub- 
served  by  two  different  types  of  movement,  the  .so-called  pendular 
and  the  peristaltic.    The  ju  tiduhir  moi;  mints  are  rendered  evi- 
dent by  allowing  tiie  intestine  to  float  out  in  a  bath  of  isotonic 
saline,  when  the  various  loops  sway  from  side  to  side  like  a  pen- 
dulum.   By  clo.ser  examination  it  can  be  .seen  that  the  movements 
are  protluced  b\    faint  waves  of  contraction  of  both  muscular 
eoats    which    sweep    with    considerable  rapidity  along  the  gut. 
When  the  waves  arrive  at  a  part  of  tlie  intestine  containing  any 
solid  substance,  they  become  accentuated,  and  this  becomes  most 
marked  at  the  middle  of  the  solid  ma.ss  of  food,  thus  tending,  on 
account  of  the  contraction  of  the  circular  fibers,  to  divide  the 
ma.ss  into  two.    They  are  therefore  sometimes  called  scijmrt,tin<i 
iiioremcnfs.    Beyond  the  mass  the  contractions  again  fade  away. 
Their  function  is  eviilently  to  break  up  the  food  mas.ses  and  thus 
mix  them  with  the  iligestive  juices.    This  can  be  very  well  .shown 
in  skiagram  shadows  of  the  abdomen  some  time  after  taking  food 


INTESTINAl;  DUiKSTIOX. 


ri) 


mixed  witli  bismuth.  A  poluimi  of  food  can  be  seen  to  divide  into 
.st'vei-al  si'Kmt'iits,  cacli  of  wiiicli  in  a  few  seconds  breaks  into  two 
tho  neighboring  halves  then  joining  tofrether.  and  the  process 
rejjeating  itself. 

Two  varieties  of  pn-isliillic  ic<iv<  s  are  usually  descrilM'd,  both 
of  which  are  charact  rized  b.v  a  marked  constriction  preceded  by 
a  distinct  dilatation  of  the  <,Mit,  v.hich  may  extend  for  a  consid- 
erable distance  down  it  'two  feet).  The  one  variety  of  wave 
travels  slowly  (i/j  f"i-  P"'i'  minute),  and  has  the  function  of  car- 
rying along  the  food:  the  other  travels  very  ra|)idly  (peristaltic 
rush),  and  is  evhleiitly  for  the  purpose  of  hurrying  along  irri- 
tating suV)stances. 

Hesides  being  .set  up  by  the  jjresence  of  food  in  the  intestine. 
the»«  waves  nuty  bo  influenced  through  the  nerxous  .system;  stim- 
ulation of  the  vagus  e.xeites  them,  wiiereas  stimulation  of  the 
sympathetic  brings  about  a  marketl  inhibition,  in  which  the  whole 
gut  becomes  i)rofoundly  relaxed  with  the  excei)tion  of  the  ileo- 
colic sphincter,  which  contr  :ets.  This  influence  of  the  splanch- 
nic may  be  excited  refl  xly,  as  by  jiain  or  fear. 

T'li  »iov('}n<  nis  of  th(  hir()(  iiitrsthn  are  more  diftieult  to  study 
than  those  of  the  snuiU  intestine.  They  vary  con.siderably  in 
different  animals,  as  indeed  is  to  be  expected  when  we  rememlH-r 
that  the  function  of  this  part  of  the  alimentary  tract  depends 
upon  the  nature  of  the  food.  In  herbivora.  for  example,  food 
nniy  lie  in  the  capacious  ca-cum  for  days,  and  even  in  carnivora. 
in  which  this  part  of  the  gut  is  rudimentary,  it  may  remain  for 
twenty-four  hours.  Jn  nmn  the  conditions  seem  to  be  intermedi- 
ate between  those  in  the  herbivora  and  carnivora.  and  the  move- 
ments are  believed  to  be  as  follo.vs:  .\s  tin  semifluid  food  en- 
ters the  ca'cum  through  the  ileo-ca'cal  valve  and  collects  in  the 
ciecum  anil  proxinud  colon,  it  excites  the  occurrence  of  waves  of 
constriction,  which  start  i)robably  about  the  hepatic  tiexure  and 
travel  back  towards  the  ea-eum.  thus  forcing  the  food  into  this 
sac  and  tending  to  cause  recurring  axi:-.!  currents  to  be  set  U|). 

Occasionally  the  arrival  of  t!ie  wave  at  the  (iccnm  starts  a 
true  peristaltic  wave,  which  t::iv;'ls  <!istally  getting  feebler  as  it 
proceeds,  and  which  nmy  carry  some  of  the  contents  into  the 


■' 


1 

ii 


so 


I'IIVsIO[,(K;v  pok  dkntai,  stiidknts. 


m^ 


tratisvorse  eoloii.  Hero  the  mass  assuriH's  more  or  loss  of  the  con- 
sistfJic-y  of  fjpcos,  when  jiiocc  pow.-i-fiil  ix-ristaltii'  waves  iiiak.' 
their  ai)|)<'araii('t'  and  carry  the  solid  masses  on  towards  the  i-ee- 
tnni.  These  waves  ai-c  suffieieiitly  eiiorgetie  to  keep  the  descend- 
ing f'olon  eoniparatively  enijjty,  and  the  fa-cal  masses  fjradnally 
aeeunn-latt  in  the  sifjiiioid  Hexure  and  rectum  until  evacuateii 
hy  the  act  of  defa'cation. 

Kxamination  of  the  ac'-ompanyiiifj  diagram  (Fifj.  7)  will  sliow 
how  louff  food  takes  to  |)ass  aionf?  tlu'  various  parts  of  the  jrastro- 
intestinal  tract. 


Fiff.    7— Iiiaunun    ..r    1,1,1.     11    mk.s    i-,i    :,    CMpsul.'    roiituiiiintr    l.isnuith    ti. 
r.:i(h  tUv  vMiiou.s  pinis  of  thf  liiiKf  im.silii.-. 


The  Absorption  of  Food. 

As  has  been  explained,  th.-  wimh'  object  of  dij?estion  is  Id  Invak 
up  the  large  molecule-  ,.f  which  f.MMJ  is  composed  into  Ntiialler 
ones  so  fiiat  they  can  he  absorbed  into  the  blood  or  hmph  which 
circulates  in  the  mucous  nx  nd)rane  of  the  intestines.  Iidess  un- 
ih'r  iuius\ml  cin-nmstances.  no  absorption  occurs  until  the  snudi 
intestine  is  reached.     H.  ro  sugars  are  absorbed  as  d.-xtnt.se,  and 


THE  ABSORPTION  OF  F(H)l). 


81 


til 


jn'oti'ius  lis  aiiiino  bodu-.-;,  into  tlic  l)loo»l.  whilst  fats  aro  absorlHMl 
into  tlic  lyini)hati('  vessels,  as  fatty  acids  and  ulyeerine.  These 
substaiK'i>s  are  absorbed  in  solution,  which  woultl  lead  us  to  ex- 
pect that,  because  of  the  water  absorbed  along  with.  them,  the 
contents  of  the  small  intestine  would  Im-  more  solid  at  its  lower 
end  than  at  its  upper  end;  but  this  is  not  the  case,  for  the  diges- 
tive juices  which  have  been  secreted  make  up  for  the  loss  of 
water.  It  is  in  the  large  intestine  that  the  water  is  finally  ab- 
sorbed. 

Attempts  have  been  maih'  to  explain  the  pi'ocess  of  absorption 
in  terms  of  the  known  laws  of  filtration,  o.snmsis,  surface  tension, 
and  ind»ibition,  but  little  further  |)rogress  has  been  made  than  to 
establish  the  fact  that  although  these  i)rocesses  may  play  a  role, 
they  do  not  e.\i)lain  the  whole  thing,  for  if  blood  serinn  be  placed 
in  an  isolated  loop  of  intestine,  it  will  become  entirely  absorbed 
even  although  identical  in  all  the  above  i)ropeities  witli  the 
blood  of  the  animal.  That  osmosis  does  have  some  influence, 
however,  is  evidenced  by  the  well-known  effect  of  a  strong 
saline  solution  in  the  intestine:  it  attracts  water  from  the  blood, 
tbus  diluting  the  intestinal  contents  and  stimulating  peristaltic 
contractions.     It  is  in  this  way  that  saline  cathartics  ai't. 

Regarding  the  absorption  of  fats,  it  is  now  definitely  kn«wn 
that  these  first  of  all  split  into  fatty  acid  and  glycerin.-  b\  th»- 
action  of  the  lipa.sc  of  i)aucreatie  .juice  The  fatty  awid  then 
unites  with  alkali  to  form  a  soap,  or  with  bile  salts  to  forw  a  s«»l- 
uble  comi>ouiid.  Jn  either  ca.se.  the  dissolved  fatty  acid  f^Mwes 
into  till'  intestinal  epithelium,  into  which  is  also  af)sort*--(1  the 
glycerine,  the  two  re-uniling  after  their  absorption  so  as  to*  form 
neutral  fat  again,  which  then  pas-ses  into  the  .-entral  lact»«l  »f 
the  villus,  whenei'  it  is  transported  h>  the  abdominal  lymphatics 
to  the  thoracic  duct,  which  discharges  it  into  the  sulx-lavian  veiii 
on  the  left  side  of  the  root  of  the  neck. 

Ifuuifir  SI  iisiitiiitis  coincide  with  stomach  contractions  which 
difl'er  from  those  oceui'i mg  fluring  <ligestion.  Thirst  is  due  to 
dryne^hs  of  the  throat,  h  is  temiiorarily  relieved  by  moistening 
this,  but  unless  li<|uid  is  swallowed  permanent  thirst  de.ilops 
because  the  tissues  Iteecune  dry. 


ResusM  <rf  iMStiMM  of  IN[g«8tiTe  EnxyiiMs. 


SiWRETIOS 


Saliva 


Enztmk  or 

AlUlNANT 
Ar,KN(  Y 


....Pts«i 
Alkaries 
Gastric  ;«*<■»'.  P«»p8in 


Ikanet 


Panel  aattk, 
juiPi"  .   . . . 


nil 


Intettinal 
juive  .  .  .. 


Bni'trrid 


«C1. 


ILipaae  

!Tryp»inogen 
Lipasr         .  . 

Amylopsin 
lAlkali 


Bl»«'  salts 


Ayoli 


EiBteroiHniisf' . 


Acting  on 
carbohyUratea 

i  Acting  on 
i  fats  .... 
Acting  on 
proteins  . 


AirioN 


ConvertB  boilwi  starcli  into  maltaev. 
Favors  mtion  of  ptyalln. 

(1)  Converts   iTM^taproteiaa    (acid   albu- 

min, etr  I   Into  9r«Ff>ns«8  ami  pep- 

tsees. 
«C'   Clots  millf. 
di   Produces  met^iroteins. 

(2)  Acts  as  antiseptic. 
i(3)  Stops  action  .«  ptyalin. 

•  Acts  on  emulsifleti  fats. 

■  Inactive  until  actwi  on  by  ent^rokinase. 
Splits   neutral   fai    titto   fatty   acid   and 

glyrerfae. 
.  Conv#-rt8  all  Marches  into  maitose. 
.  (1)   Helps  to  neutralize  HCl  of  chyme. 
(2)  Combines  with  fatty  aeid  t©  form 
soaps. 

.   n     Augmeai:  'tie   action   ni    lipase  and 
and  asyioiHBn. 
(i)   Precipitate  pHpstn  and  peptoaet^  in 

chyme. 
I  (31  Combines  wrA  fatty  iKdds. 

■  (1)  HidpH  to  ueuttKlize   SIM  of  chyme 
1(2)  Cjambineu   with    tatr-    acid   to   rorni 

iMSPS. 

Converts      trypsinogeii      into      trypsin. 

which  splits  proteins  into  amino 

UcKlieB. 
'nn verts  caseiiiuicen  and   peptones   into 

simple  amino  bodies. 
(Jne     for    each     disaccharide.     splittinR 

them   into  monosaccharides. 
(Both    the  last   two  enzymes   are   more 

plentiful   in    (he   epithelium   than 

in   the  intestinal  juice.) 
(1)   Digest  cellulose. 
(-)   Splits   monosaccharides    into   lactic 

and  lower  acids. 


Split  higher,  into  lower  fatty  acids. 

Split    off    aromatic    groups,    as    phenol, 
cre-iol,  et?. 

(Besides  these  specific  actions,  bacteria 
:  may  perform  many  of  the  diges- 

j  tive  functions  of  the  juicei   i 


m^. 


CHAPTER  VITT. 

METABOLISM. 

The  Energy  Balance. 
Introductory.— The  objcet  of  digestion,  iis  wo  have  seen,  is 
to  render  the  food  capable  of  absorption   into  the  eireuhitory 
fluids,  the  blood  and  lymph.     Tlie  absorbed  food  pnKlnets  are 
then  transported  to  the  various  organs  and  tissues  of  the  bo<ly. 
wher;"  the>    may  l)e  eith.  r  usid  or  stored  away  against  future 
requireft*ents.    Afte>-  bein^;  used,  certain  su>»stanees  are  prmlueed 
as  waste  products,  and  these  pass  l)aek  into  the  bltKKl  to  be  <'ar- 
ried  to  the  orjfans  of  excretion,  by  which  they  are  expelled  from 
th-  h«Hay.     IJy  eomparison  of  the  amount  of  tiiew  t-xeretory  pi'od- 
ucts  with  that  of  the  constituents  of  food,  we  can  tell  how  much 
of  the  latter  lias  been  retained  in  ihe  l>ody.  or  lost  from  it.    This 
constitutes  the  subject  of  ijrut  nit   mftdholisfii.     (hi    the    other 
haml,  we  may  direct  our  attention,  not  to  ihe  baiaiire  betw   -n 
intake  ajid  output,  but  to  the  cheiiiical  i-lian>res  tiiroush  winch 
each  fooiistuflfs  miust  pas.s  between  its  alworption  and  excretion. 
This  is  the  subject  of  sptcial  m'taboUsui.     In  the  one  case  we 
content  oui's«'lves  with  a  conipar»t4(n  of  the  raw  material  which 
is  ac(|uired  and  tlie  tinished  pro<tuct  which  is  prinlueed  by  the 
animal  factory;  in  the  other,  we  *'ek  to  b-arn  something  of  the 
particular  changes  to  wliii-ij  "adi  crude  [.eovluct  is  subjected  be- 
fore it  can  Ih-  used  for  tiie  uurposc  of  driving  tiw  machinery  of 
life  or  of  repairing  th.'  worn  o»T  pans  of  the  bmJy. 

In  drawing  up  si«-li  a  balancr  lAieet  of  general  metabolism,  we 
must  select  for  comparison  substances  whicli  are  common  to  both 
intake  and  output.  In  g<  nt  ral  the  intake  comprises.  l>f'si.i.->  oxy 
gen.  the  proteins,  fats  ami  c.irbohydrates.  and  th.'  output,  carbon 
dioxide,  water  and  the  various  nitrogenous  constituents  of  urine. 
This  dissimilarity  in  chemical  stnnture  ijctweeu  the  substances 
ingest,  d  and  those  excreted    lindts    us,    in    bulaneing    the    one 


84 


PIiySIOLOGY    FOR    DEXTAL    STl'DENTS. 


Jiifiiiiist  tile  otli.T,  to  a  coniiiarison  of  the  siiuillcst  frajriiifiits  into 
wiiicli  cacli  can  he  l)mkfii.  Thi-sc  arc  tlic  elements  and  of  them 
carbon  and  nifrop-ii  aiv  the  only  ones  wliicli  it  is  possildc  to 
nieasuro  with  accuracy  in  both  intake  and  output.  From  bal- 
ance shtM'ts  of  intake  and  outi)ut  of  carlmii  and  nitrogen  and 
from  information  obtained  by  observinjj  the  i-atio  between  the 
amounts  of  oxygen  consumed  by  the  animal  and  of  carbonic  acid 
(CO.)  exci-eted.  we  can  draw  far-reacliing  conclusions  regaru  ^ 
the  relative  amounts  of  protein,  fat  and  carbohydrate  which  liave 
been  involved  in  the  metabolism.  As  lias  already  been  stated, 
the  essential  nature  of  the  metaboli<'  process  in  animals  is  one 
of  oxidation,  that  is  to  say.  one  by  which  large  unstable  mole- 
cules are  broken  down  to  those  that  are  simple  and  stable.  Dur- 
ing this  ])rocess  of  katabolism,  as  it  is  called,  the  potential  energy 
which  is  locked  away  in  the  large  molecules  beccmies  lilx-rated 
as  actual  or  kinetic  energy,  that  is  to  say,  as  movement  and  heat. 
It  therefore  becomes  of  importance  to  conij)are  the  actual  energy 
which  an  animal  expends  in  a  given  time  with  the  energy  which 
has  nieanwiiile  been  rendered  available  by  metabolism.  This  is 
called  the  »  n<  rtjii  balanc, .  We  .shall  first  of  all  consider  this  and 
then  proceed  to  examine  somewhat  more  in  detail  the  mutt  rial 
hdhnia  of  the  bodif. 

« 

Energy  Balance. 

The  unit  of  energy  is  the  large  calorie  (written  C).  which  is 
the  amount  of  heat  reipiin  d  to  raise  the  temjH-rature  of  one  kilo- 
gramme of  water  tiirongli  one  degree  (Centigrade)  of  tempera- 
ture.' We  can  determine  the  calorie  value  by  allowing  a  meas- 
ured i|uantity  of  a  sub.stance  to  burn  in  comj)res.se<l  oxygen  in 
a  steel  bomb  which  is  placed  in  a  known  volume  of  water  at  a 
certain  temperature.  Whenever  condjustion  is  c()mi)leted.  W( 
find  out  through  how  many  degrees  the  temperature  of  the  water 
has  b«'come  raised  and  niidtiply  tliis  by  the  volume  of  water  in 
litres.     .Mea.sured   in  sucli  a  caloi'imeter,    as    this    a])paratus    is 


nh.'  (nsluutiiin  li.  twcpii  a  raUnlc  .iii.l  a  .It-tji.-i'  of  t.TniKiaturi-  must  \>r 
clearly  uiiii.r.Mtiiiiil.  Th.-  fumifi-  ...xpit  !-s.'.m  iiinnilili/  of  mtuiil  hciit  .■iicrKv  • 
tlif  iHlter  merely  tells  u.h  llie  iiiteii.-dty  iit  which  the  heat  eneigv  is  Wing  Kivcn 


THE  ENEUiOV   BALANCE. 


85 


callfd,  it  lias  bt'cii  fouiul  that  thi-  number  of  caloiii-M  lilicrattil 
by  buriiiiip  one  gramiiR'  of  each  of  tlic  proximate  priiicipk-s  of 
food  is  as  follows : 

,.,,,,      \  Staroli   4.1 

(  arhonvdratt'S  ■'     ,  ,  ,, 

/   Sufrar    4.0 

Protein .'>.() 

Fat  0.:{ 

Tile  same  number  of  calories  will  be  liberated  at  whatever  rate 
tiie  eombustion  i)ro<'eeds,  i)r()vide(i  it  n'sults  in  tlie  same  end 
l)ro<luc'ts.  When  a  substane*-.  sueii  as  supar  or  fat.  is  burneil  in 
the  i)res«'nee  of  o.\ypen.  it  yields  carbon  dioxide  an<l  water,  which 
are  also  the  end  i)roducts  of  the  metabolism  of  these  foiulstutl's 
in  the  animal  body:  therefore,  when  a  tjramme  of  siipar  or  fat 
is  (juickly  burned  in  a  calorimeter,  it  releases  the  same  amount 
of  energy  as  when  it  is  slowly  oxidi/ed  in  the  animal  body.  But 
the  case  is  ditferent  for  proteins,  beea\ise  the.se  yield  le.ss  com- 
jdetely  oxidized  end  products  in  the  animal  body  than  they  yield 
wlien  burned  in  oxysreii ;  so  that,  to  ascei'tain  the  i)hysi()lii<rieal 
energy  value  of  protein,  we  mu.st  d<'dui't  from  its  physical  lieat 
value  (calories  1  the  physical  heat  value  of  the  incompletely  ox- 
idized enil  products  of  its  metabolism,  it  is  obvious  that  we  cnn 
compute  the  total  available  energy  of  our  diet  by  multiplying 
tiu'  ipiantity  of  each  foodstuff  l)y  its  calorie  value. 

In  oi'der  to  measure  the  ener-gy  wliicli  is  actually  liberated  in 
the  animal  body,  we  must  also  use  a  calorimeter,  but  of  some 
what  different  eiiiistiMiction  from  that  used  by  the  chemist,  for 
we  iiave  to  provide  for  long  ctHitinued  observations  and  foi'  aii 
uninterrupted  su}  j>i,\  of  oxygen  t.i  the  animal.  Aiii}>iii!  'fhtr 
itiiit<r.'i  are  also  usually  provided  with  means  foi'  tlu-  :  . 'Wire- 
ment  of  the  amount"*  di'  <-atl>on  dioxide  (and  water)  'li»eli  r,,red 
ami  of  oxygen  afiwiHM-  hy  tin  animal  during  the  «l)st  i  \,-- .  >n. 
Su<"h  respiration  calm  ■»«  ters  iiave  been  oiade  lor  ail  sorts  of  mi- 
?nals.  the  most   iwrft***!   t'i*r  hw  on  man   having  lt<-"ii  i-i«iisi  nieti'd 

in    Anierieii    (see    K«    Si         As    ill  list  rating  the   extreme    !ie«'Uracy 

of  even  the  iaTTfcsl  .»!•  rln-s*'  i-  .s  iileresrtH^  to  note  tli.-'t  tin  act 
ual  iieat  give     (lut   xkwu  ii  ikauite  amount  of  alcohol  or  ether  is 


86 


PHYSIOLOGY   FOB   DENTAL   STIOENTS. 


burned  in  one  of  them  exactly  corresponds  to  tli<'  amount  as  meas- 
ured by  the  smaller  bomb  calorimeter.  All  of  the  enerRy  liber- 
ated in  the  body  does  not,  however,  take  tiie  form  of  heat.  A 
variable  amount  appears  as  mechanical  work,  so  that  to  measure 
in  calories  all  of  the  energy  which  an  animal  .expends,  one  must 
add   to   the   actual  calorifs  nivcn  out.  the  caloric  ci|uivalcnt  of 

T 


□  m 

KiS-  S. — Diagram  of  Atwater-Bcni'dirt  I'esiiiiiilion  CiiIdi  imtlrr.  .\y  ;hi' 
animal  u.sps  up  tlip  <>-,  the  total  volumi*  of  air  Hliiinlc.s.  Tliis  .shrlnkaKi'  is  liuli- 
cated  by  thf  metiT,  uml  a  lorrfspoiiiiiiiK  uinoutit  of  i  >..  i.s  il<liviri-il  from  tin; 
weigiied  Oj-eylinder.  Tin-  iiiiriusc  in  Wfi^lit  of  liottl.s  II  and  III  ^fi\<'S  me 
CO,.. 

the  muscular  work  wiiicli  lias  hccii  iK'rfoniicd  by  the  aiiiinnl 
(luring  the  pci'iod  of  obstTvation,  Tliis  can  be  iiica.siiicd  by 
means  of  an  er},'oiiictcr.  a  calorif  ('(iir-csixnidiiitr  to  42")  kilo- 
gramme" metres  of  work.  That  it  has  Imm'u  possibU-  to  strike  an 
accurat<'  balance  bctwccji  the  infiikc  and  \\h'  output  of  energy 
of  the  animal  body,  is  oiii'  of  flic  achicvfini'iits  of  iiiotlcni  "'xpcri- 
iiii'iital  bioloiiv.      It   can  be  done  in   tlic  ca.sc  of  the  hninaii  ani- 


;A  kiloRrammtnK  tri>  is  the  product  of  the  load  in  iciiograiunu  s   l)y  the  dis- 
tiou-i-  In   nielre.s  throuKh   which  it  is  lifted. 


TlIK    KNKRUY    BAI.ANCK. 


87 


inal;  tlius,  a  man  (loiii^  work  on  a  bicyclf  crfjoiiu'tcr  in  tin-  l><iu- 
diet  paloriiiietcr  jrave  out  as  actual  litat,  4.s:{:!  <'..  and  ilid  work 
(•(nialling  ()02  ('.,  Kivinj?  a  total  of  :>A'-i'>  <"  H.v  drawing  np 
a  balance  sheet  of  his  intake  and  output  of  food  material  <lnrin^ 
this  period,  it  was  found  that  tiie  man  liad  consumed  an  amount 
capable  of  yielding  r),4.V.»  ('.,  wWwh  may  he  considered  s  ex- 
actly balancing  the  actual  outt)ut. 

Having  thus  satisfied  ourselves  as  to  the  extreme  accuracy  of 
the  method  for  nieasurini?  energy  output,  we  shall  now  cotisider 
some  of  the  conditions  which  control  it.  To  study  these  we  must 
first  of  all  determine  the  basal  hint  produclioti,  tliat  is,  tlie  small- 
est energy  outi)ut  which  is  compatible  with  iiealth.  This  is  as- 
certained by  allowing  the  nuin  to  sh-i'p  in  the  calorimeter  and 
then  measuring  his  calorie  outi>ut  while  lie  is  still  resting  in  bed 
in  the  morning,  and  fifton  hours  after  the  last  meal.  When 
the  results  thus  obtained  on  a  nund)er  of  individuals  are  calcu- 
lated so  as  to  repr«icnt  the  calorie  output  i)er  kilogranune  of 
lH)dy  wt  ight  i'l  each  case,  it  will  be  found  that  1  C.  per  kilo  per 
hoTir  is  di.scharged.  That  is  to  say.  the  total  ent  rgy  expen«liture 
in  24  hours  in  a  man  !,f  70  kilos,  which  is  a  good  average  weight, 
will  be  70X24  =  1,()80  (". 

When  food  is  taken  the  heat  production  rises,  the  increase  over 
the  basal  heat  production  amounting  for  an  oidiniry  diet  to 
about  ten  i)er  cent.  Besides  being  the  ultinmte  source  of  all  the 
body  heat,  food  is  therefoic  a  direct  stinudant  of  heat  pnMluction. 
This  specific  dynamic  action,  as  it  is  called,  is  not,  however,  tiie 
same  for  all  groups  of  foodstuffs,  being  greatest  for  prott-ins  an<l 
least  for  carbohydrates.  Thus,  if  a  starving  afdma!  is  given  an 
amount  of  protein  which  is  eijind  in  calorie  value  to  the  calorie 
outjiut  dui"  <r  starvation,  the  caloric  output  will  increase  by  30 
per  cent.  icreas  with  carbohydrates  it  will  increase  only  by 
()  per  cent.  Evidently,  then,  protein  liberates  much  free  heat 
during  its  assimilation  in  the  aninud  body;  it  burns  with  a  hot- 
ter flame  than  fats  or  carbohydrates,  although  as  in  the  ease 
«»f  fats,  at  h'jwt,  before  it  is  comi»Ietely  burnt,  it  nuiy  not  yield  .so 
much  energy.  This  peculiar  property  of  proteins  accounts  for 
their  well-known  heating  (lualities.    It  explains  why  protein  com- 


tsw»j 


m 


88 


PlIVKIor^XtV    FOR    DKNTAI,    STt'DlNTS. 


pow'H  NO  larK*'  n  proportion  (»f  tli."  (li«-t  of  peoples  liviii«  in  cold 
n-gions.  and  why  it  is  cut  down  in  tin-  diet  of  those  who  dwell 
near  the  tropics.  Individiuds  maintained  on  a  low  protein  diet 
may  suffer  intensely   from  the  cold. 

If  we  add  to  the  basal  heat  pro<incti..ii  of  1  <iH()  ('.  another 

168  r.  (or  lu  i)er  eent^  on  a uint  of  food,  the  total  1,H4H  C. 

nevertheless  falls  far  short  of  that  which  we  know  must  he  lilwr- 
nt  I  when  we  calculate-  the  available  energy  of  the  diet.  What 
iH'comcs  of  the  e.xtra  fuel .'  The  answer  is  that  it  is  used  for 
musnilar  work.  Thus  it  has  been  found  that  if  the  observed 
person,  instead  of  lying  down  in  the  calorimeter,  is  made  to  sit 
ill  a  ciiiiic.  the  he:it  pnidiation  is  riised  by  S  \uv  cent,  or  if 
lie  i)erfuniiN  ^iich  moveriietits  as  woulil  be  m cessary  for  onlinary 
work  I  writing  at  a  desk),  it  may  ri-<.  :".)  per  cent,  that  is  to  my, 
to  90  (■  i  tr  hour.  .Mlowing  ><  liouis  .or  sb'cp  a-u!  1»;  hours  for 
work,  we  can  thus  accotint  lor  2.1«S  (',.  tiie  remaining  :{()()  odd 
('.  Mhich  is  reiiuind  to  bring  the  total  to  that  which  we  know, 
from  statisticMl  tables  of  the  diets  (»f  such  workers,  to  b.'  the 
actual  (iaiiy  ex|M'nditure.  In-iiig  due  to  the  exercise  of  walking 
If  the  exer.'is-'  be  more  strenuous,  .still  more  calories  will  Ik-  ex- 
pended: thus,  to  ascend  a  bill  of  l.ti.jO  feet  at  the  rate  of  'J.7 
miles  an  hour  reipiires  407  e.xtra  calories.  Field  workers  may 
e.xjiend,  in  24  hours,  almost  twice  as  nuiny  calories  as  those  en- 
gaged in  sedentary  occupations. 

.\nother  factor  which  controls  the  energy  output  is  the  cool- 
ing influ(u<(  of  (h,  atmosiihtn.  When  this  is  marked  more 
heat  must  be  liberated  in  order  to  maintain  the  body  t. mp -rature 
(see  p.  135).  In  otiier  words,  the  necessary  heat  loss  must  be 
compensated  by  an  increa.sed  heat  i>roductioii,  just  as  we  nuist 
burn  more  coal  to  keep  the  house  at  a  given  temperature  on  a 
cold,  lliau  on  a  warm.  day.  This  ad.ju.stment  of  energy  liberation 
to  the  rate  of  cooling  at  the  surface  of  the  body  explains,  among 
other  things,  wiiy  it  should  be  that  small  animals  give  out  mudi 
more  energy,  per  unit  of  ImkIn  weight,  than  thus.-  thai  are  larger. 
The  small  aninud  has  relatively  the  great,  i-  surface  area,  just 
as  twoctd)es  of  (Mjual  weight  when  brought  together  have  a  com- 
bined weight  which  is  double  that  of  tither  cuiie.  but  a  surface 


TIIK    K.NKUliV    BAr.AVCK. 


S!> 


area  which  is  Ichs  tliaii  iloiihh'  (twn  siirfiUfs  hiivin>»  hiiii  Itrou^ht 
toKftlicr).  Its  Kft'iitcr  tfiKimi'v  ti»  fool  cxithiiiis  why  siiiitll  iitii- 
iiuiIh  witwiM  HO  much  more  quickly  sucoumh  to  cold  thau  tlioHc 
that  arc  lar^cf.  ainl  why  slim  persons  bIhhiW  led  the  cold  more 
keenly  than  those  that  are  stout. 

Other  thinjTs.  sucli  as  diet,  external  tem|ieratiu'e.  etc.  bein^ 
the  same,  it  is  therefore  siirftin  unn  ami  iiul  h<»hf  ivrif/ht  wh'hh 
(li  trrmiiii  s  Ihi  i  ik  rt/n  jiroilm  lion,  a  tact  wliicli  is  clearly  deiii- 
onstrate<l  by  tindinjr  that  tin-  calorie  oMt|tut  lor  ditTereiit  animals 
is  constant  when  it  is  calculated  for  each  sijuarc  metre  of  sur 
face.  Thus,  a  liorsc  produces  only  14.r»  C.  per  ku'.  of  body 
weight  in  24  hours,  whereas  a  mouse  produces  4.V2('..  but  if 
wo  calculate  accordin>f  to  square  metre  of  surface  tin-  dif 
fereiices  practically  vanish.  These  facts,  however,  do  not  apply 
when  the  dilTcrences  in  size  arc  due  to  a^e.  This  fai-t  has  been 
imwt  strikiiiRly  dtMuonstrated  in  the  case  of  man.  for  it  has  been 
found  that  the  calorie  requirenient  per  unit  of  surface  is  very 
<listinctly  greater  in  the  early  years  of  life  than  later.  Thus,  tak- 
ing the  discharjje  of  carbon  di<»\iile  as  a  "riterion  of  the  ener>ry 
ilischarfje.  the  followin-;  results  have  been  obtained  from  indi 
vi<iuals  sitting  down  : 

CiiImiii    diiiNiilc    ili-1'hiirui'il.    Ik'T 

...lUiiif   iiK'Iii    i>f   .iiirfiiif 

,inil  li'Mir   (uraiiinii-s) 


2».!t 
26.5 
23.5 
21.8 
18.5 
I6.!t 
!«.:{ 
14.2 

26.6 
20.1 
16.0 
14.8 
16.3 
17.!t 


\\i'l'iii:t'   iiui' 

.\\iTiii:i'  »fi«lil 

( \i';irs) 

Ikiliiur.'iiiiiiii'si 

Mtllrx 

!t  2  :■. 

28 

12   1   2 

34 

1.1   1   2 

51 

lit   1  2 

fiO 

25 

68 

36 

68 

45 

77 

58 

85 

h'liiml'S 

8 

22 

12 

36 

1.-. 

4!t 

17  2  :; 

54 

30 

54 

45 

67 

Ui  |2B 

tii 

itt  1^ 

l£ 

^  1^ 

lEg 

Ibl 

1.4 

il.6 

MICROCOPY  RESOLUTION  TEST  CHART 

NATIONAL  BUREAU  OF  STANDARDS 

STANDARD  REFERENCE  MATERIAL  1010a 

(ANSI  and  ISO  TEST  CHART  No.  2) 


90 


PHYSIOLOOY   FOB   DENTAL   STUDENTS. 


TJiis  table  shows  us  clearly  that  over  and  above  the  greater 
combustion  necessary  on  account  of  their  relatively  greater  sur- 
face, children  require  calories  for  growth.  They  must  be  fed 
more  liberally  than  adults,  otherwise  they  starve.  The  table 
further  shows  that  boy.  must  be  more  liberally  fed  than  girls  of 
ecjual  age  and  body  weight,  probably  because  of  their  greater 
restlessness.  It  is  on  account  of  these  greater  food  requirements 
that  children  are  the  first  to  die  in  famine. 


CHAPTER  IX. 

■  METABOLISM  (Cont'd). 

The  Material  Balance  of  the  Body. 

We  must  distinguish  .between  the  balances  of  the  organic  and 
the  inorganic  foodstuffs.  From  a  study  of  the  former  we  shall 
gain  information  regarding  the  sources  of  the  energy  production 
whose  behavior  under  various  conditions  we  liave  just  studied. 
From  a  study  of  the  inorganic  balance,  although  we  shall  learn 
nothing  regarding  energy  exchange— for  such  substances  can 
yield  no  energy— we  shall  become  ac<iuainted  with  several  fact^ 
of  extreme  importance  in  the  maintenance    of    nutrition    and 

growth. 

To  draw  up  a  balance  shed  of  organic  intake  and  output  re- 
quires an  accurate  chemical  analysis  of  the  food    and    of    the 
excreta  (urine  and  expired  air).    Furnished  with  such  analyses 
we  proceed  to  ascertain  the  total  amount  of  nitrogen  and  carbon 
in  the  excreta  in  a  given  time  and  to  calculate  from  the  known 
percentage  of  introgen  in  protein  how  much  protein  must  have 
undergone  metaboli.sm.    We  then  compute  how  much  carbon  this 
quantity  of  protein  would  account  for,  and  we  deduct  this  from 
the  total  carbon  excretion.    The  remainder  of  carbon  must  have 
come  from  the  metabolism  of  fats  and  carbohydrates,  and  al- 
though we  cannot  tell  exactly  which,  yet  we  can  arrive  at  a  close 
approximation  by  observing  the  respiratory  ([uotient   (R.  Q.), 
which  is  the  ratio  of  the  volume  of  carbon  dioxide  exhaled  to 

that  of  oxygen  retained  by  the  body  in  a  given  time,  i.  t'-,— 

When  carbohvdrates  are  the  only  foodstuff  undergoing  metabol- 
ism the  quotient  is  one,  that  is  to  say,  W-  CO,  excretion  and  O, 
intake  a-e  equal  in  volume.  The  reason  for  this  is  that  a  molecule 
of  carbohydrates  consi.sts  of  C.  along  with  II.  and  0.  in  the  same 
proportions  as  they  exist  in  water;  therefore  oxygen  is  re(iuired 

91 


92 


PHYSIOLOGY   FOB   DENTAL   STl'DENTS. 


^1 


la 


f 

[r 


to  oxidize  the  C,  but  not  the  H.,  and,  since  e(|uimolecular  (,uan- 
tities  of  all  gases  occupy  equal  volumes  (at  the  same  tempera- 
ture and  pressure),  the  volume  of  CO,  produced  equals  the  vol- 
ume of  C.  require<l  to  produce  it.  The  conditions  are  other- 
wise  in  the  case  of  fats  and  proteins,  for  besides  C.  these  mole- 
cules contain  an  excess  of  II.,  so  that  O.  is  required  to  oxidi/e 
some  of  the  H.,  as  well  as  all  of  the  C.  A  greater  volume  of  O, 
IS  therefore  absorbed,  diiriner  their  combustion  than  the  volume' 
of  CO,  that  is  produced,  and  R.  Q.  is  about  0.7.  My  observing 
this  quotient,  then-fore,  we  can  approximately  det.-rmine  the 
source  from  which  the  non-i)rotein  carbon  e.xcretion  is  derived. 
Having  in  the  above  manner  computed  how  inudi  of  each  of  the 
pim'mate  principles  has  undergone  metabolism,  we  next  pro- 
ceed to  compare  intake  and  output  with  a  view  to  finding 
whether  there  is  an  cjuilibrium  between  the  two.  or  whether  re- 
tention or  loss  is  occurring. 

Starvation.— In  order  to  furnish  us  with  a  standard  condition 
with  which  we  may  compare  others,  we  will  first  of  all  study  the 
metabolism  during  starvation.     When  an  animal  is  starved,  it 
has  to  live  on  its  own  tissues,  but  in  <loiiig  .so.  it  saves  its  protein 
so  that  the  excretion  of  nitrogen  falls  after  u  few  days  to  a  low 
level,  the  energy  re.|uirements    being    meanwliih.    supplied,    as 
mucli  as  possible,  from  stored  carboliydrate  and  fat.    Althougli 
always  small  in  comparison  wit'    fat,  the  stores  of  carbohydrate 
vary  considerably  in  different  animals.     They  are  much  larger 
in  man  and  the  herbivora  than  in  the  carnivora.     Diiriiifj  thr 
first  f(w  (lays  of  starvation  it  is  common,  in  the  herbivora,  to 
find  that  the  excretion  of  nitrogen  is  actually  greater  than  it  was 
before  starvation,  because  the  custom  has  become  established  in 
the  metabolism  of  these  animals  of  using  carbohydrates  as  the 
main   fuel   material,   so   that   when   this  fuel  is  withheld,  as  in 
starvation,  proteins  are  used  more  than  before  and  the  nitrogen 
excretion  becomes  great.-r.     We  may  say  that  the  herbivorous 
animal  has  become  carnivorous.     The  same  thing  may  occur  in 
man  when  the  previous  diet  was  largely  carboliydratr. 

During  the  greater  part  of  starvation,  however,  nio.st  of  the 
energy  re(iuired  to  maintain  life  is  derived  from  fat    as  little 


STARVATION". 


«»:'. 


h</^M^ 


jis  i>ossiblf  bi'iiif?  (Icrivt'tl  from  pi'otciii.  This  {y\tv  of  iiu'tabolisiii  yj'  ^j[j^ 
liists  until  all  liif  available  rcsourct's  of  fat  have  Ik-coiiic  i-x- 
hausted,  wlivii  a  iiion'  cxtoiisivt-  iiictabolisni  of  protfiii  sets  in 
with  the  coii8t'<|Ui'iiec  that  the  iiitro}?eii  cxcrt'tion  rises.  This  is 
really  the  harbinger  of  death — it  is  often  ealled  the  prouurtnl 
I'ine  in  uUrugen  tsvntion.  It  means  that  all  the  ordinary  fuel 
of  the  animal  economy  has  been  used  up.  and  that  it  has  become 
necessary  to  burn  the  very  tissues  themselves  in  order  to  obtain 
sufficient  energy  to  maintain  life.  Working  capital  being  all 
exhausted,  an  attempt  is  made  to  keep  things  going  for  a  little 
longer  time  by  li(|uidation  of  pernmnent  assets,  liut  the.se  as.sets, 
as  rei)resented  by  protein,  are  of  little  real  value  in  yielding  the 
desired  energy  because,  as  we  have  seen,  oidy  4.1  calories  are 
available  against  f)..'{,  obtainable  froi  fats.  These  facts  exj)lain 
why  during  starvation  a  fat  man  excretes  daily  less  nitrogen 
than  a  lean  man,  and  why  the  fat  man  can  .stand  the  starvation 
for  a  longer  time. 

Not  only  is  there  this  general  saving  of  protein  during  .star- 
vation, but  tliere  is  also  a  discriminate  utilization  of  what  has 
to  be  used  by  the  ditferent  organs  according  to  their  relative 
activities.  This  i^  very  clearly  shown  by  comparison  of  the  loss 
of  weight  which  each  organ  undergoes  during  starvation.  The 
heart  and  brain,  which  nuist  be  active  if  life  is  to  be  maintained, 
lose  only  about  Ji  per  cent  of  their  original  weight,  whereas  the 
voluntary  nniscles,  the  liver  and  the  spleen  lose  lU.  'A  and  67 
l)er  cent,  respectively.  No  doubt  some  of  tliis  loss  is  to  be  ac- 
counted for  as  due  to  the  disapi)earancc  of  fat,  but  a  sufficient 
remainder  represents  protein  to  make  it  plain  that  tiiere  mu.st 
have  been  a  mobilization  of  this  substance  from  tissues  where  it 
was  not  absolutely  necessary,  such  as  the  liver  and  voluntai-y 
muscles,  to  organs,  such  as  the  heart,  in  whicii  energy  transfor- 
mation is  sine  qua  non  of  life.  The  vital  organs  live  at  the  ex- 
pense of  those  whose  functions  are  accessory. 

When  "e  compare  the  excretion  of  carbon  dioxide  from  day 
to  day  during  starvation,  it  will  be  fount!  to  remain  practically 
constant  when  calculated  for  eacl-  '  'logram  of  body  wi  irht.  The 
same  is   rue  for  the  calorie  outpui     Certain  unusual  substances 


,  I 


r 


)4     ly**'   *         PHYSIOLOGY   FOR   DENTAL   STUDENTS. 

such  as  crcatiii  also  make  tlieir  appearance  in  tlie  urine,  anil 
there  is  an  increase  in  the  excretion  of  ammonia,  indicating  that 
larger  rjuantities  of  free  acid  are  heing  8«'t  free  in  the  organism. 

Starvation  ends  in  death  in  an  adult  man  in  somewhat  over 
four  weeks,  but  much  sooner  in  children,  because  of  their  more 
active  metabolism.  At  the  time  of  death  the  body  weight  may 
be  reduced  by  50  per  cent.  The  body  temperature  does  not 
change  until  within  a  few  days  of  death,  when  it  begins  to  fall, 
and  it  is  undoubtedly  true  that  if  means  be  taken  to  prevent  cool- 
ing of  the  animal  at  this  stage,  life  will  be  prolonged. 

Normal  Metabolism. — Apart  from  the  practical  importance 
of  knowing  something  about  the  behavior  of  an  animal  during 
starvation,  such  knowledge  is  of  great  value  since  it  furnishes  a 
standard  with  which  to  compare  the  metabolism  of  animals  tmdcr 
normal  conditions.  Taking  again  the  nitrogen  balance  as  indi- 
cating the  extent  of  protein  tear  and  wear  in  the  body,  let  us 
consider  first  of  all  the  conditions  under  which  equilibrium  may 
be  regained.  It  would  be  quite  natural  to  suppose  that  if  an 
amount  of  protein  containing  the  same  amount  of  nitrogen  as 
is  excreted  during  starvation  were  given  to  a  starving  animal, 
the  intake  and  output  of  nitrogen  would  balance.  We  are  led 
to  make  this  assumption  because  we  know  that  any  business  bal- 
ance sheet  showing  an  excess  of  expenditure  over  income  could 
be  met  by  such  an  adjustment.  But  it  is  a  very  different  matter 
with  the  nilfogen  balance  sheet  of  the  body;  for,  if  we  give  the 
starving  animal  just  enough  protein  to  cover  the  nitrogen  loss, 
we  shall  cause  the  excretion  to  rise  to  a  total  which  is  practically 
e(iual  to  the  starvation  amount  plus  all  that  we  have  given  as 
food,  and  although  by  daily  giving  this  amount  of  protein  there 
may  be  a  slight  decline  in  the  excretion,  it  will  never  come  near 
to  being  the  same  as  that  of  the  intake.  The  only  effect  of  such 
feeding  will  be  to  prolong  life  for  a  few  days. 

To  strike  equilibrium  we  must  give  an  amount  of  protein  whose 
nitrogen  content  is  at  least  two  and  one-half  ti-.es  that  of  the 
starvation  level.  For  a  few  days  following  the  establishment  of 
this  more  liberal  diet,  the  nitrogen  excretion  will  be  far  in  ex- 
cess of  the  income,  but  it  will  gradually  decline  until  it  corre- 


NORMAL    MKTABOMSM. 


95 


spoiids  to  the  intake.  Having  once  gaine<l  an  oquilibnuin,  we 
may  raise  its  level  by  gradually  increasing  the  protein  intake. 
During  this  progressive  raising  of  the  protein  intake,  it  will  be 
found,  at  least  in  the  carnivora  (eat  and  dog)  that  a  certain 
amount  of  nitrogen  is  retained  by  the  body  for  a  day  or  so  imme- 
diately following  each  increase  in  protein  intake.  The  excre- 
tion of  nitrogen,  in  other  words,  does  not  immediately  catch  u)) 
on  the  intake.  The  amount  of  nitrogen  thus  letaiued  is  too  great 
to  be  accounted  as  a  retention  of  disintegration  products  of  pro- 
tein ;  it  must  therefore  be  due  to  an  actual  building  up  of  new 
protein  tissue,  that  is,  growth  of  muscles. 

Such  results  undoubtedly  obtain  in  the  eat,  and  less  markedly 
in  the  dog.  But  they  do  not  do  so  in  man  and  the  herbivorous 
animals.  In  these,  we  can  never  give  a  sufficiency  of  protein 
alone  to  maintain  nitrogen  etiuilibrium ;  there  will  always  be  an 
excess  of  excretion  over  intake.  But  indeed  it  scarcely  recjuires 
any  experiment  to  prove  this,  for  it  is  self-evident  when  we  con- 
sider that  there  are  only  400  C.  in  a  pound  of  lean  meat,  and 
there  are  few  who  coidd  eat  more  than  4  pounds  a  day,  an  amount 
which  however  would  only  furnish  about  half  of  the  required 
calories.  A  person  fed  exclusively  on  flesh  is  therefore  being 
partly  starved,  even  although  he  may  think  that  he  is  eating 
abundantly  and  be  (luite  comfortable  and  active.  This  fact  has 
a  practical  application  in  the  so-called  Banting  cure  for  obesity, 
which  consists  in  almost  limiting  the  diet  to  flesh  and  green 
vegetables,  allowing  only  a  very  small  quota  of  carbohydrates 
or  fats. 

Very  different  results  are  obtained  when  carbohydrates  or  fats 
are  freely  given  with  the  protein.  Nitrogen  eiiuilibriui  can 
then  be  regained  on  very  mueli  less  protein,  so  we  speak  oi  fats 
and  carbohydrates  as  being  "protein  sparcrs."  Carbohydrates 
are  much  better  protein  sparers  than  fats ;  indeed  they  are  so  effi- 
cient in  this  regard  that  it  is  now  commonly  believed  that  carbo- 
hydrates are  essential  for  life,  so  that  when  the  food  contains  no 
trace  of  carbohydrates,  a  part  of  the  carbon  of  protein  has  to  be 
converted  into  this  substance.  Tliis  important  truth  is  supported 
by  evidence  derived  from  other  fields  of  investigation  (e.  g.,  the 


m 


I'JlV^KtLOGY    FOR    DKNTAL    ^TIDKNTS. 


HI 


I'l  :'t 


iM'lifivior  of  diabetic  p.ificnfs,  wliciv  the  |  iwcr  lo  iikc  ciirholiy- 
(Iratcs  is  iniicli  lii-pi-csscd  ).  The  iiiiirkod  protciii-sparin^r  ncfioii 
of  carbohydriitfH  is  iilustr-Hti'd  in  another  way,  iiaiiifly.  by  tlie 
fact  that  we  can  fji-catly  diminish  the  protein  break-down  during 
starvation  hy  ffWinn  carbohydrates,  hi  tliis  way  we  can  indeed 
reduce  the  daily  nitroj^en  excretion  to  about  oiu'-third  what  it  is 
in  complete  starvation. 

In  tlu'  case  of  man  livinj;  on  an  average  diet,  althougli  the 
daily  nitrogen  excretion  is  aliout  1.')  granunes,  it  can  be  lowered 
to  about  6  granuiies  provided  that  in  place  of  the  protein  that  has 
l)een  removed  from  the  diet  enough  carbohydrate  is  p'  en  \■^  bring 
tlie  total  calories  iij)  to  the  normal  daily  reipiiremi    ■  tcess 

of  carbohydrate  over  these  energy  rei|uiremen-:  ,i    the 

I)rotein  may  be  still  further  red\iced  and  yet  e(|  .    lin- 

tained.  To  do  this,  however,  it  is  not  the  amoiii  .  .  irbohy- 
drate  alone  that  determines  the  ease  with  which  the  irrrdmibU 
protriii  minium))!  can  be  reached  ;  the  kind  of  i)rotein  itself  makes 
a  very  great  difference.  This  has  been  very  beautifully  shown 
by  one  investigator,  who  first  of  all.  determined  liis  nitrogen  ex- 
cretion while  living  on  nothing  but  starch  and  sugar,  and  then 
proceeded  to  see  how  little  of  diffei;^it  kinds  of  pi-otein  he  had 
to  take  in  order  to  bring  himself  into  nitrogenous  e<|uilibrium. 
He  found  that  he  had  to  take  the  following  amounts:  :W  gr.  meat 
jirotein.  'M  gr.  n.ilk  protein,  M  gr.  rice  protein,  liH  gr.  i)otato 
protein,  r)4  gr.  bean  i)rotein.  76  gr.  bread  protein,  and  102  gr. 
Indian  corn  protein.  Tlw  organism  is  <'videiitly  able  to  satisfy 
its  i)rotein  demands  when  it  takes  meat  protein  much  more 
readily  than  with  vegetable  i)roteins. 

To  understand  vh>/  p)-ofci)is  shoidd  vtn-n  so  )HU(h  in  //»,/> 
)iii(rifii'c  vitlut,  we  must  examine  their  ultinuite  structure  very 
closely.  When  the  ])rotein  molecule  is  disintegrated,  as  by  diges- 
tion, it  yields  a  great  iminber  of  nitrogen-containing  acid.s,  the 
amino  acids,  as  well  as  several  bases  and  aromatic  substances. 
The  most  important  of  these  acids  are  glyein.  alanin,  serin,  valin. 
leuciii,  prolin,  aspartic  and  glutamic  acids,  the  bases  being  lysin. 
histidin  and  arginin  and  the  aromatic  bodies,  phenylalanin,  tyro- 
sin  and  tryptophan.     These  substances  constitute  the  available 


NOKMAI.    MKTAI'OI.ISM. 


97 


"units"  or  "btiiltHiiK  stoiifs"  of  protein  niolt'ciilcs,  but  in  no 
two  proteins  an-  the  inaterials  used  exactly  in  the  same  propor- 
tions, some  proteins  liaviuK  a  preponderanee  of  one  or  more  and 
an  absenee  of  otiiers.  just  as  in  a  row  of  houses  there  may  be  no 
two  that  are  exaetly  alike,  allhouph  for  all  of  them  the  same 
building  materials  were  available.  Albumin  and  globulin  are 
the  most  important  i)roteins  of  bloml  and  tissues,  so  that  th" 
food  m\i.st  contain  the  necessary  units  for  their  construction.  If 
it  fails  in  this  regard,  even  to  the  extent  of  lacking  only  one  of 
them,  the  organism  will  either  be  unable  to  construct  that  pro- 
tein, and  will  therefore  suffer  from  partial  starvation,  or  it  will 
have  to  construct  for  itself  this  mi.ssing  unit,  a  process  which  it 
can  accomplish  for  some  but  not  all  of  the  above  list. 

It  is  therefore  api»arcnt  that  tho««»  proteins  are  most  valu- 
able as  foods  that  contain  an  array  of  units  which  can  be  reunited 
to  form  all  the  varieties  of  protein  entering  into  the  structure 
of  the  body  i)roteins.  Naturally,  the  protein  which  most  nearly 
meets  the  re(|uirem«'nt  is  meat  prot<'in,  so  that  wc  arc  not  sur- 
pris«'d  to  fiiid  tliat  less  of  it  than  of  any  other  jirotein  has  to  1m? 
taken  to  gain  nitrogen  equilibrium.  ('as«'in.  tne  protein  of  milk, 
although  it  does  not  contain  one  of  the  most  important  units, 
namely,  glycin,  is  almost  as  good  as  meat  protein,  because  tlit 
organism  is  itself  able  to  manufacture  glycin.  When,  on  the 
contrary,  proteins  such  as  zein  from  corn  are  given,  in  which  cer- 
tain units  are  missing,  starvation  inevitably  ensues.  liut  it  does 
not  do  so  if  the  missing  unit,  which  in  the  case  of  zein  is  trypto- 
phan, is  added  to  the  diet. 

These  n)ost  important  facts  have  been  ascertained  by  experi- 
ments carried  out  in  New  Haven  by  O.sborne  and  Mendel. 
Young  albino  rats,  just  weaned,  were  fed  on  a  basal  diet  con- 
sisting of  the  sugar,  fat  and  salts  of  milk  to  which  was  added 
the  protein  whose  nutrition  value  it  was  desired  to  study.  The 
rats  were  weighwl  frc  a  day  to  day.  and  the  results  plotted 
as  a  curve — the  nirvc  of  growth.  A  gradually  rising  curve 
was  obtained  when  casein  or  the  albumin  of  milk  or  eggs,  or 
the  edestin  of  hemp  se:>d,  or  the  glutenin  of  wheat  was  fed, 
but  this  was  not   the  case  with  the   gliadin   of  wheat   or,   a.s 


98 


I'llVSlOtXWY   P(»B  PENTAf,   HTl'DENTS. 


above  mentioned,  with  zein  of  corn.  It  will  be  wen,  there- 
fore, that  of  the  two  proteins  in  wheat  one,  gluteiiin,  contains 
all  t  le  .("cessary  units  for  building  up  the  growing  tissues,  but 
that  in  the  other  protein,  gliadin.  some  essential  unit  is  absent; 
by  analysis  this  was  found  to  be  lysin.  By  adding  lysin  to 
glifldin  a  normal  curve  of  growtli  resulted,  thus  showing  that 
this  was  really  the  missing  unit.  The  result  was  made  even  more 
spectacular  by  feeding  a  batch  of  young  rats  on  gliadin  alone, 
so  that  they  remained  undeveloped  and  stunted,  and  then  adding 
lysin  to  their  diet,  when  they  very  <|uiekly  made  up  for  lost  time, 
and  soon  reached,  if  not  (juite,  yet  aim  ♦  as  gooil  a  developm^int 
as  their  more  fortunate  brothers  who  h  i  b«>en  fed  on  glutenin 
or  casein  from  the  very  start. 

The  animal  economy  itself  can  therefore  protluce  certain  of 
the  amino  bodies — thus,  as  we  liave  seen,  it  can  pro<luce  glycin — 
this  power  being  much  more  developed  in  the  case  of  herbivor- 
ous as  compared  with  carnivorous  animals.  In  the  vegetable 
food  on  which  oxen  live  several  of  the  prominent  amino  bo<lies  of 
muscle  protein  are  missing,  but  they  are  constructed  in  the  or- 
ganism by  altering  the  arrangement  of  the  molecules  of  thow^ 
amino  bodies  which  are  present,  so  that  a  j  rotein  is  built  up 
which  is  very  like  that  present  in  the  tissue  of  the  carnivorous 
animals.  Even  in  the  case  of  the  herbivora,  however,  there  are 
limitations  to  the  power  of  forming  new  amino  bodies.  Trypto- 
phan cannot  be  formed  in  this  way,  for  example. 


T'l 


CHAPTER  X. 
THE  SCIENCE  OK  DIKTKTICS. 

In  order  that  a  proper  assortment  of  amino  bodies  may  be 
assured  in   the  diet,   protein   is  taken   in   fxeess  of  tlie   (juan- 
tity    necessary   to  n-puir  tlie  tissues.     It    has    been    thou^bt 
by  some   that    the   surplus   thus   talicii    by    tlie    average    in<li- 
vidual  is  nnieh  nu)re  than  Ufcd  be,  and  that  an  unneet'ssary  strain 
is  thus  thrown  on  the  orKUiis  whieh  bave  to  dispose  of  llie  .'xees^ 
It  has  been  elaimed  by  the  adherents  of  ihis  view  that  naiiy  ot 
the  ob.scure  sym[)toms — beadaehes.    mnseular    atul    bac      i)ains. 
sleepiness,  ete.— that  eity  folk  are  liable  to  sufV.  ••  fiw      are  diK 
to  the  presence  in  the  blood  of  uniit'ct'8.sary  by-products  of  ex- 
cessive protein  metabolism.     Such  opinions  seemed   to  rec.'iv.' 
very  weighty  indorsemept  some  years  ago  when  Chittenden  pub- 
lished a  long  series  of  observations  showing  that  men  in  varii)us 
callings  in  life,  could  perform  their  daily  work  (juite  satisfac- 
torily and  apparently  maintain  their  health  after  reducing  the 
protein  of  their  diets  to  less  than  half  of  the  usual  amount.    No 
direct  benefit  could  be  claimetl  for  this  reduction  except  that 
some  of  the  men  believed  that  they  felt  better  and  fitter  an«l 
more  inclined  for  work,  an  improvement  whieh    admits   of    no 
quantitative  measurement  because  of  the  p.HVchological  elements 
involved.      Even   althougb   these   observations   were   conducted 
with  all  the  care  and  accuracy  of  the  highly  trained  scientist, 
they  bave  been  considered  quite  iimde(|uate  to  justify  the  claim 
that  man  takes  too  much  protein,  but  the  observations  have  been 
of  immense  value  in  compelling  a  careful  review  of  the  evidence 
that  the  proportion  of  jirotein  whieh  habit  lias  j)rescribed,  as 
being  the  proper  one  for  us  to  take,  is  really  the  most  suitable 
for  our  daily  needs. 

There  are,  however,  diffrrDicrs  in  the  prntdn  content  of  the 
diet  according  to  the  race  and  environment.  This  has  been  as- 
certained by  compiling  the  stardard  diet  for  a  community,  that 

99 


I 


100 


I'llYNIflUNtY    FOR   PENTAIi   STIDKNTH. 


1 


rololn 

Fat 

Carbo. 

Total  Cal 

.     C. 

N. 

gr. 

KT. 

Rr. 

ft- 

ir. 

118 

56 

500 

3.(»45 

328 

18.8 

151 

46 

522 

3.190 

340 

24 

133 

115 

429 

3.400 

... 

21.3 

187 

•27 

775 

4.900 

... 

30 

100 

100 

240 

2.324 

230 

16 

in.  nu'nsuririK  the  exact  )|UHiititii>s  of  proti'iii  niul  carbohydrnto 
ill  the  diets  wliieli  the  people  are  aceiiHtoiiUMl  to  live  nii,  and  aver- 
affiiiK  the  reHultM.  (hie  reimirkahh-  oi'teome  of  siieh  NtatiNtieal 
work  haH  iH-eii  to  Hhow  that  for  |H-ople.s  living  under  approxi- 
mately the  same  eonditions  as  rejraivlH  elimate  and  aiiioiint  of 
daily  museiilar  work,  the  aveni^e  daily  rei|iiiremeiit  of  ealories. 
carbon  and  nitrogen  works  out  pretty  much  the  same.  altiiou(;li 
there  may  Ik'  some  diversity  in  the  proportions  of  protein  aiuj 
carbohydrate.     The  following  table  shows  this: 

Type  of  individualB.        Pi 

Average  workman  in 

Germany,  20  years  age. 
Oerman  soldier  in  the 

Held   

British  soldier  in  peace... 
UuBsian  soldier  in  war  (Man- 

rhurian  campaign )  .  . . . 
Professional  man   

Such  fipures  can  be  compiled  with  tolerable  accuracy  because 
the  diet  is  under  control.  It  is  of  course  more  difficult  to  collect 
sufficiently  accurate  data  rej^ardiiiR  the  diets  of  civilians,  but  it 
is  safe  to  say  that  the  average  city  dweller  in  temperate  zones 
derives  his  daily  requirement  of  15  gr.  nitrogen  in  95  grammes 
of  protein,  which  also  yields  60  gr.  of  the  reipiired  2.'»0  gr.  car- 
bon. This  deficit  he  might  supply  either  from  fats  or  earbohy- 
di'iates,  the  actual  proportion  dejM'ndiiig  on  availability  and  price. 
It  should  be  particuliirly  noted  that  the  |)roporti()n  of  j)rotein  is 
very  much  increased  whenever  strenuoiJs  muscular  work  has  to 
Ix'  performed.  Now  the  (|uestion  is.  do  such  .statistical  studies 
substantiate  Chittenden  "s  claim  that  the  protein  which  we  are 
accustomed  to  consume  could  profitably  b<!  reduced?  They  cer- 
tainly do  not.  Let  us  for  a  moment  consider  the  health  condition 
and  physical  dev«'lopment  of  communities  such  as  the  Uengalis 
of  Lower  Bengal,  who  live  largel\  on  rice,  and  take  only  a  little 
less  in  the  way  of  protein  than  what  Chittenden  would  have  us 
take.  The  body  weijrht.  chest  measurement  and  muscular  devel- 
opment are  distiuetly  iufitior  to  those  of  the  natives  of  Eastern 


DIETKTICS. 


101 


Tk>iiKii1.  wlio  howcviT  Im'Ioiik  to  tlio  SHiiie  rnct'  ns  \hv  Idwci'  Ilfii 
KiiHs,  l»nt  (lifft-r  from  them  in  taking  iiion'  prott'iii  in  tlifir  f«M)«l 
Not  only  this,  but  tl  m'  people  arc  in  every  wnw  of  the  word 
half  starved,  and  tiuy  are  very  prone  tt>  diseas*-,  espeeially  of 
the  kidneys,  the  very  type  of  dis«'as«'  whieh  we  are  tol<l  -xeesNive 
j.rotein  consumption  must  predispose  to.  Dialtetes  is  also  veiy 
prevalent  ainonfi^st  these  people,  probably  beeuuHc  of  the  enoriii- 
ous  quantities  of  suKMr-yieldiiiR  foo<l  (c.irbohydrates)  whieh  they 
arc  compelletl  to  cat  in  onler  to  provide  sufficient  calorics  for 
life.  They  can  not  y  t  fat.  nor  do  they  desire  it.  Mentally,  hey 
arc  a  \  -y  inferior  ■.  This  then  is  an  experiment  on  a  nueh 
ftrantlcr  seal-  than  ittenden's.  and  what  of  the  results.'  It 
is  fortumit*'  mat  most  of  Chittenden's  subjects  '•thronjjh  force 
of  circum8t>i!ic(,.  "  have  returned  to  their  old  dietetic  habits. 

f..;aclly  co  ■  .'dant  results  have  been  obtained  when  attempts 
h  '  been  made  to  reduce  the  protein  in  the  dietaries  of  [)ublic 
institutions  such  as  prisons,  alms  houses,  etc  There  has  invari- 
ably been  a  di-stinct  increase  in  the  sick  list,  especially  of  such 
diseases  as  inieumonia.  tulM-rculosis,  etc.  And  if  wc  .seek  for 
evidence  of  an  oi)posit«'  nat'iie.  wc  do  not  find  that  excess've 
protein  ingestion  is  fraught  with  any  evil  consei|Uences  to  the 
community.  Thus  the  Kskinm  takes  five  times  more  protein  tiian 
the  Jicngali  and  two  and  one-half  times  more  than  the  Kuroi)ean. 
and  yet  he  is  peculiarly  free  from  "uric  acid  '  diseases;  and  his 
l)hysical  endurance  and  his  power  of  withstanding  cold  arc  ex- 
traordinary, and  there  is  no  i|uarre!ingl 

Tliere  are  a  great  man.v  .st'condar;.  factors,  sucli  as  nvailabilily. 
ta.stc,  etc.,  that  determine  the  average  diet  of  a  conununity,  l)ut 
the  main  determining  factors  arc  instinct  and  experience.  In 
the  struggle  for  existence  between  human  races,  we  ma.v  a.ssnme 
that  adequacy  of  diet  has  played  a  role  ami  that  the  average 
which  is  taken  rcj)resents  that  which  conduces  to  the  greatest 
efficiency. 

We  have  dealt  at  some  length  on  those  (piestions  because  of 
their  great  ractical  imi)ortancc,  and  because  they  .show  us  that 
in  the  matter  of  the  protein  content  of  our  diet,  as  in  that  of  all 
other  animal  functions,  there  comes  into  pluy  the  princij)l('  of 


102 


PHYSIOLOGY   FOB   DENTAL   STUDENTS. 


If  ' 

i'i 


the  "factor  of  safety."  We  have  two  lungs,  although  it  is  quite 
possible  to  live  with  one  only,  two  kidneys,  although  one  will 
usually  suffice,  and  so  with  protein  in  food,  we  could  get  alon^' 
for  some  time  with  about  half  of  wiiat  we  take,  but  at  the  con- 
stant risk  of  a  deficiency,  for  should  physical  exhaustion  occui-. 
a  reserve  of  building  stones  ouglit  1o  be  available  to  restore  the 
tissue  which  has  been  consumed.  Instead  of  the  excess  of  pro- 
tein throwing  a  strain  on  the  organism,  the  contrary  is  the  casi', 
for  it  is  indisputably  a  greater  strain  for  the  tissues  to  have  to 
construct  new  building  stones  than  to  us(>  these  supplied  ready 
made  in  the  food. 

Another  deduction  which  we  may  «lraw  from  these  observa- 
tions is  that  more  protein  should  be  taken  when  its  source  is 
mainly  vegetable  food  than  wh.n  it  is  animal.  On  the  other 
hand,  there  is  nothing  to  indicate  that  one  kind  of  animal  pro- 
tein possesses  any  advantages  over  another;  fiesh  protein,  milk 
protein,  egg  protein  are  practically  of  eijual  dietetic  value,  and 
with  regard  to  what  varieties  of  meats— whether  light  or  d;ii-k— 
are  most  luitritious,  all  we  can  say  is  that  any  ditferences  that 
may  be  thought  to  exist  are  not  due  to  differences  in  the  chemical 
nature  of  the  proteins  which  they  contain,  but  depend  on  their 
flavor  and  digestibility.  There  are  more  fads  and  fancies  about 
what  meats  are  nutritious  and  what  are  not  so  than  would  fill  a 
volume,  but  after  all  the  whole  question  is  one  of  flavor.  ^Man 
digests  best  what  he  likes  best,  and  he  thrives  best  when  digestion 
is  good.  Doctors  and  dentists  must  be  i-eady  to  discuss  ([uestions 
of  diet,  for  the  public  likes  to  be  treated  with  something  more 
than  the  hard  facts  of  science;  he  demands  something  mystical 
and  mysterious  besides:  if  he  agrees  to  be  fed  according  to  calorie 
and  protein  values,  he  demands  besides  that  he  be  told  fairy 
tales  about  some  peculiar  virtiies  which  this  or  that  vai-iety  of 
foodstuff  possesses. 

Very  practical  conclusions  may  be  drawn  from  tlies«>  observa- 
itons  regarding  the  most  suiluhlr  du  t  {or  1h<  <il)i  dweller.  It  is 
evident  that  we  are  now-a-days  in  pos.session  of  a  sufficient 
amount  of  scientific  infornuition  regarding  both  the  daily  re(|uire- 
nients  of  the  body  and  the  ability  of  the  various  foodstuffs  to 


DIB?rETICS. 


103 


fulfill  these  requirements,  to  compute,  from  the  market  prices  of 
foods,  how  much  it  should  take  per  diem  for  an  individual,  or  a 
family  of  individuals,  to  live  healthfully  and  economically.  The 
day  will  surely  come  when,  through  the  medium  of  schools  and 
the  press,  everyone  will  know  what  we  nuiy  call  the  fundamentals 
of  dietetics,  namely:  (1)  that  a  man  of  sedentary  occupation 
(the  ordinary  city  clerk)  requires  daily  2,600  calories,  and  a 
laboring  man,  at  least  11,000  calories.  (2)  That  at  least  5  per 
cent  of  the  calories  should  be  provided  in  protein  food  of  animal 
origin  (meats,  milk)  with  10  per  cent  or  more  as  other  protein 
(bread,  oatmeal,  etc.). 

To  enable  the  housewife  to  purvey  the  necessary  food  to  meet 
these  re(iuirements,  she  must  therefore  become  familiar  with  the 
calorie  value  and  the  percentage  of  protein  in  the  different 
classes  of  protein  foods,  and  of  the  calorie  values  of  other  great 
staples  of  diet.     Canned  foods  will  no   doubt   some    day    have 

printed  on  the  label :    "This  can  contains calories,  of  which 

per  cent  are  in  proteins  of  grade "    And  this  is  no 

Utopian  idea;  it  is  practical  common  sense.  The  adoption  of 
such  a  scheme  is  far  more  likely  to  be  the  solution  of  the  problem 
of  the  high  cost  of  living  than  anything  else,  for,  indeed,  it  is  not 
so  much  the  high  cost  of  living  as  it  is  the  cost  of  high  liviiK? 
that  troubles  us.  We  demand  business  efficiency  in  our  manufac- 
turing organizations,  and  yet  we  ai'c  inclined  to  ridicule  as  im- 
practical any  attempts  at  nutritive  efficiency  in  the  animal  organ- 
ization, which  is  our  own  body.  Not  only  the  principles  of 
dietetics,  but  the  details  as  well  are  now  so  thoroughly  under- 
stood that  their  application  in  the  feeding  of  the  masses  is  only 
a  matter  of  education.  Dietery  impostures  of  the  meanest  de- 
scription, often  hiding  behind  a  ''bluff"  of  scientific  knowledge, 
are  of  course  the  most  serious  enemies  we  shall  have  to  face  in 
spreading  the  knowledge.  It  will  be  the  duty  of  physicians,  of 
dentists,  and  of  the  educated  classes  to  offset  this  conunercial 
brigandage  by  spreading  the  gospel  of  food  efTRciency. 

As  illustrating  the  food  eflficiency,  in  relationship  to  cost  we 
may  take  the  following  table  from  the  menu  of  a  well-known 
restaurant  company : 


104 


niYSIOLiMiY    FOK    DKNTAI,    !-Ttl)KNTS. 


Cost 

in  cents 

per  portion 

Bread   5 

Apple  pie 5 

Boston  pork 

and   beans   15 

Ham  sandwich  ...  5 

Corn  beef  hash ...  15 

Beef  stew 15 

Club  sandwich  ...  25 

Sliced  pineapple  ..  5 

Mayonaise    20 


Calories 

Calories 

Cost 

Total 

',;  In 

for  5  cents 

in  cents 

protein 

per  1000 
calories 

933 

12 

933 

5 

337 

5 

337 

15 

828 

12 

276 

18 

170 

20 

170 

30 

507 

14 

170 

30 

461 

25 

154 

32 

409 

20 

82 

61 

36 

46 

36 

138 

53 

16 

13 

35 

(I.tisk) 


The  above  table  is  not  by  any  means  from  a  cheap  restaurant. 
liy  economy  and  judicious  purchasinfj  it  is  possible  even  in  New 
York  to  purchase  1.000  calories  having  the  i)roper  proportion  of 
calories  for  8  cents,  so  that  a  working  nmn  may  easily  cover  his 
dietetic  re«|uirements  for  2")  cents  a  day,  exclusive  of  the  cost  nl 
cooking.    All  he  spends  above  this  is  for  personal  taste  and  relisli. 

Chemistry  of  the  Commoner  Foodstuffs. 

The  accompanying  diagram  (Fig.  !))  indicates  the  composition 
of  some  of  the  commoner  foods  and  is  wlf-explanatory.  TIktc 
are  certain  foodstuflFs  concerning  wiiich  a  little  more  detail  ma\ 
however  be  advisable. 

Wheat  Flour,  besides  a  large  amount  of  starch,  contains  two 
proteins,  glutein  and  gliadin.  When  the  flour  is  mixed  with 
water  and  then  kneaded,  it  forms  dougli.  because  the  proteins 
change  into  a  .sticky  .substance  called  gluten.  As  dough  the  tlour 
is  not  a  suitable  food,  because  the  digestive  .juices  cannot  pene- 
trate it.  To  render  it  digestible  the  dough  must  Ix'  made  porous 
and  this  is  accomi)lished  by  causing  bubbles  of  carbon  dioxide 
gas  to  develoj)  in  it.  either  by  mixing  it  witli  baking  powdi'r 
which  is  com[)osed  of  a  bicarbonate  and  an  organic  acid  (tar- 
taric) or  by  keeping  it  in  a  warm  place  witii  yeast,  which  fer- 
!uents  the  sugar  that  is  jiresent.  The  sugar  is  developed  from 
the  starch  by  the  action  of  the  dia.sta.se  (see  p.  44)  |>resent  in 
the  flour. 


1(1         21) 


3(1       4"      r>(p       fi"       ""       *>"       " 


1SS5 


:ui(i 


(I      iiiii 

~n  Wluilc  milk 


"j  Skim   mil 


( Mn'csc. 


r.utlir. 


\vci;in«'  mill'    '  ("i»  ). 

AviiiiKf   million    (raw). 
AvciMKi'   P'lik    (  niw). 
l-'isli — lloiiinlir    (liiw). 

Hncon. 

Whciit    Ixi'Mil. 


Ash   iiiid   water. 


mm 


</,,,J////\       I'riitriii  nf   l.st   Quality. 


I'rotcin  of  2n<l  guality. 


Kilt. 


Carlioliydratp. 


ralorirs. 


Ki^'     !(.— I)i."t..ti<-    chart.    showinB    th..    |..Mv...,taKr    amounts    of    th.>  variou."* 

proximat.-  prin.ipl.  s    ( in.li.atr.      .y  the  shadfil  aivas)   an.l  th.-  calori  ( imli- 

rat.<J  in  r.'.l )   vi.-lil.-,!  Hy  hurnin.    1    lli    of  th..  .•ommon-r  f.MMlsiuffs.       .  num- 

iHTS  to  th,'  riKht   r.i,ivs..nt   th.>  .■ah.ri..  yalu.s  an.l   Hi.'   nain.s  t..  th.'  m  li.   th.- 
food    in   (iU(>»lion. 


DlETfVnCS. 


105 


Wh-ii  tlu"  voast  has  bocn  allow.-d  to  act  Un-  sonu-  time,  or  if 
bakiii«  i)ow<l."r  was  us...l,  wl.cii  the  ^as  formation  lias  c.-ascl.  suit- 
able portions  (loaves)  of  doufrh  are  placed  in  the  oven.  The  heat 
eauses  the  inclosed  bubl)les  of  jras  to  expand  so  that  the  wlu^le 
mass  becomes  aeratcil  and  further  increase  of  temperature  acts 
on  the  proteins  and  starches  on  the  surface  coajfulatins  the  tor- 
imr  and  converting,'  the  latter  into  d.-xtrins.  Thus  is  the  crust 
formed,  lirown  bread  is  iiia.le  from  wheat  from  which  all  the 
husk  has  not  Vkh-u  removed.  There  are  two  possible  advanta-es 
of  this  over  white  bread,  namely,  th.-  husks  act  as  a  mild  laxative 
and  the.v  seem  to  contai'i  traces  of  vitamines  (see  j).  121). 

Other  Cereals.— TlH'se  include  mai/e  or  Indian  corn,  oatmeal 
and  rice,  and  differ  from  wheat  in  that  their  proteins  do  imt  form 
srluten  when  mixed  with  water.    They  cannot  therefore  be  foriiie.l 
hito  bread  unless  they  be  mixed  with  some  wheat  flour.    They  are 
relatively  rich  in  ash  and  mai/e  contains  a  larjje  proi)ortinn  of 
fat.    When  rice  composes  a  lar^e  proportion  of  the  .liet,  as  is  the 
case  in  tropical  countries,  tlie  un|)or!she(!  variety  should  be  used 
to  supplv  the  vitamines.     When  the  diet  is  a  mixed  one,  however. 
daiiMfer  of  an  insufficiency  of    vitamines    <'aiiiiot    <  vjst.     As  has 
been  already  explained,  the  protein  of  cereals  is  n         '  Hrst  <|Ual- 
ity,  because  it  do.-s  not  contain  ail  of  the  amino  i.      s  (buildiiifl 
stones)  of  tissue  proteins. 

Milk  and  Milk  Preparations.— Whole  milk  is  as  nearly  as 
possible  a  perfect  food,  for  its  protein  is  of  the  Hrst  quality  and 
it  contains  a  sufficiency  of  fats  and  carbohydrates  for  the  p'owth 
of  the  tissues.     Where  muscular  exercise-  must  also  be  perforiiuMl, 
carbohv.lrates  shcmld  be  added  to  the  milk,  and  this  is  best  ac- 
complished by  tile  use  of  cereals.     Milk  is  an  economical  food, 
for  one  .luart  nearly  cMuals  in  nutritive  value  a  i)ouiid  of  steak 
or  eifjht  or  nine  cKfis,  aiul  is  easily  digested  and  assimulated,  but 
somewhat  constipating     The  chief  protein  of  milk  is  caseino^eii 
(phospho  protein)    and   is  characterized  by  beiii«  precipitat.-d 
by  weak  acids  and  by  the  action  of  jjastric  .juice.  When  milk  soui-s 
some  of  the  milk  su^ar,  or  lactose,  becomes  converted  by  bacterial 
action  into  lactic  acid  and  this  pivcipitates  caseinofjen.     When 
ail  extract  of  the  mucous  nu'inbraue  of  the  stomach  is  added  to 


106 


PIIYSIOLOOY   FOR  DENTAL   STUDENTS. 


milk  ami  tlit;  mixture  kopt  warm,  the  elot  which  forms  is  caHed 
casein.  Hy  separating  the  casein  and  allowing  it  to  stand  for 
some  time  ferments,  derived  from  moulds  and  bacteria,  act  on 
it  to  produce  chrisf.  The  cheese,  besides  ca.sein,  contains  much 
fat  and  minei-al  matter.  Cheddar  cheese  is  esj)ecially  rich  in  fat. 
Cheese  is  a  \ery  concentrated  article  uf  diet  and  when  taken  in 
moderation  is  thorotighly  digested  and  jussimiiated. 

Cream  consists  of  tlie  milk  fats  with  some  of  the  constituents 
of  milk.  It  is  the  most  easily  a.ssimilated  of  all  tlie  fats  and  is 
hence  very  nuti'itious.  When  sweetened,  flavored  and  frozen  it 
forms  ice  cream,  which  sliould  not  be  regarded,  as  it  usually  is, 
as  a  luxurv,  but  as  a  highly  nutritious  food.  It  should  not  there- 
fore suryirise  the  indulgent  parent  when  a  child  goes  off  its  food 
after  \"isiting  the  corner  pharmacy.  On  standing,  cream  ripens 
(undergoes  diange  due  to  Iwcterial  growth)  and  if  it  be  churned 
the  fat  .separates  as  buttn:  Tliere  is  no  footlstuff  that  contains 
more  calories  and  k-sides,  the  butter  contains  certain  vitamines. 
The  fluid  from  which  the  butter  separates,  hutlcrmilk,  contains 
practically  no  fat  and  is  acid  to  the  taste  because  of  bacterial 
action  on  the  lactose  producing  lactic  acid.  Its  influence  on  the 
nature  of  bacterial  growth  in  the  intestines  has  alr.ady  been 
referred  to. 

Sggg. — The  only  point  we  need  emphasize  is  tlie  much 
greater  i)ercentage  of  fat  substances  (lipoids)  in  the  yolk  than 
in  the  white.  One  dozen  eggs  equals  in  food  value  two  pounds 
of  meat.    Eggs  are  therefore  more  costly  than  milk. 

Meats. — The  building  stones  of  the  protein  molecule  of  meat, 
for  reasons  which  are  obvious,  are  more  nearly  identical  witli 
those  of  the  tissues  of  man  than  are  those  of  any  other  food.  The 
carbohydrate  is  however  insufficient  in  ;  mount,  for  which  rea- 
son we  take  potatoes  witli  meat.  The  flavors  of  different  meats 
depend  largely  on  the  extractive  substances  which  they  contain. 
These  include  creatin  and  purine  substances.  When  a  decoction 
of  meat  is  evaporated  to  small  bulk,  after  precipitating  all  of  the 
protein,  meat  extract  is  prepared,  which,  like  coffee  or  tea,  has 
no  nutritive  value  but  acts  as  a  mild  stimulant  (caffein  and  theine 
are  chemically  very  closely  related  to  the  purine  bodies  of  meat 


DIETETICS. 


107 


,.xtra*-1)      Cl.>ar  souj.s  aro  mainly  dilute  solutions  of  moat  »'X- 
tractivc-s,   but   in   beef   t.-a.  .if   properly   ma<le,   tberc   is   n.u.-h 

meat  protein.  , , 

Other  Foods  and  Condiments.-AltbouKl.  Rr.-en  veRotables 
and  salads  consist  very  largely  of  water,  tbc^y  are  very  nnportant 
artielcs  of  diet,  beeause  tl.ey  contain  ..ellulose,  wlneli  serves  to 
hu-rease  the  bulk  of  the  intestinal  eontents-to  serve  as  ballast 
as  it  were-an<l  prevent  eonstipatio.i  by  keeping  the  n.testnml 
musculature  active.  Son.e  vegetables,  such  as  spinach,  are 
..specially  important  since  they  contain  iron.  Salads  have  a 
further  imp  .rtanee  because  of  the  oil  taken  with  them.  The  rel- 
ishes and  the  condiment  flavors  are  by  no  means  ins.gnihcant 
adjuncts  of  di.-t  for  they  give  the  relish  to  f.md  without  which 
digestion  is  likelv  to  be  inefficient.  This  n...st  important  prop- 
erty of  diet  lias  been  sufficiently  insisted  upon  elsewhere. 


CHAPTER  XI. 
SPECIAL  METABOLISM. 

Hut  wo  must  now  return  to  the  more  theoretical  aspe<'ts  of  our 
subject.  We  will  proceed  to  trace  out  very  briefly  the  interme- 
diary stages  in  metabolism  through  which  proteins,  fats  and  car- 
bohyilrates  have  to  pass  in  order  to  yield  the  energy  re<iuired 
to  drive  the  animal  machine  and  to  supply  material  with  which 
to  repair  the  bi-oken-down  tissues. 

Metabolism  of  Proteins. — We  must  follow  the  amino  bodies 
after  their  absorption  into  the  blootl  until  they  ultinmtely  reap- 
pear, the  nitrogen  among  tiie  nitrogenous  constituents  of  urine 
and  the  carbon  as  part  of  the  carbon  dioxide  of  ex|)ired  air.  In 
order  to  do  this  it  is  ncces.sary  for  us  to  become  familiar  witli 
fhc  uoturc  and  source  of  tht  iirinarij  siibsfnnccs  which  contain 
nitrogen,  and  to  consider  some  of  the  most  important  chemical 
relationships  of  tliese  substances,  so  that  we  nmy  understand  how 
they  become  formi»d  in  the  body.  The  substances  in  (piestion  are : 
urea,  ammonia,  creatinin,  the  purin  bmlies,  and  undetermined 
nitrogenous  substances.  T'rea  and  ammonia  may  be  considered 
together. 

Urea  and  Ammonia.— There  is  no  doubt  that  it  is  as  anunonia 

that  the  nitrogen  of  the  amino  bodies  is  set  free  in  the  organism. 

The  free  ammonia  would,  however,  be  highly  poisonous,  so    iuit 

it  immediately  becomes  combined  with  acid  substances  to  form 

harmless  neutral  salts.     The  acid  whicli  is  ordiiuirily  used  for 

tins  pur|)ose  is  carbonic,  of  which  there  is  always  plenty  in  the 

blood  and  ti.ssue  juices.    The  ammonium  carbonate  thus  formed 

Ix'comes  changed  into  urea  by  removal  of  the  elements  of  water 

from  the  molecule,  thus: 

OH      ONH, 

/  / 

2MI    +  CO        =  CO        —  H,0 

\  \  ' 

OH       OMI, 

Ammonia  Carbonic  Ammonium 

acid  eurboiiate 

108 


NH. 

.Ml, 

/    ' 

/ 

CO        —  II. o  = 

=  CO 

\ 

\ 

OMI, 

Ml. 

Ammonium 

Urea 

earbumale 

TIIK   MF.TAB<»MSM  OP  I'KOTKINS. 


1(M) 


The  coMVersion  of  aiimioiiiuiii  carboimtf  occurH  larK^ly  in  tin- 
livor.     Our  cvi.l.'ni-t'  for  this  is:      (1)    If  solutions  coiitaiiiinK 
ammonium  carboiuitf  bo  miuU'  to  circulate  through  an  v\i-'m>i\ 
livci.  urea  is  foinu-d.     (2)   If  this  organ  th'  seriously  tlainajftMl. 
citht'r  experimentally  or  by  disease,  less  urea  and  more  ammonia 
ai)l)ear8  in  the  urine.     We  see  therefore  that  urea  is  formed  in 
order  to  prevent  the  poisonous  action  of  ammonia.    But  the  am- 
monia may  be  more  usefully  employt'd;  instead  of  iM-inj?  com- 
bined with  carbonic  acid  in  order  that  it  may  be  got  rid  of,  it 
may  be  employed  to  neutralize,  and  thus  render  harmless,  any 
other  acids  that  make  their  ap|)earance.     Thus,  it  nmy  be  em- 
ployed to  neutralize  the  acids  which  sometimes  result  during  the 
metabolism  of  fat,  as  in  the  disease,  diabetes;  or  the  lactic  acid 
that  ar)pears  in  the  muscles  during  strenuous  nuiscular  exercise ; 
or  the  acids  prmluced  on  account   of   inadequate    oxygenation. 
Taking  acids  by  the  mouth  has  a  similar  effect;  thus  the  am- 
monia excretion  rises  after  drinking  solutions  containing  weak 
mineral  acids. 

Ammonia  is.  of  course,  not  the  only  alkali  which  is  available 
in  the  organism  for  the  purpose  of  neutralizing  acids.  The 
fixed  alkalies,  sodium  and  potassium  are  also  used.  Thus.  whei. 
we  greatly  increase  the  proportion  of  these,  as  by  taking  alkaline 
drinks,  or  by  eating  vegetable  foods,  the  ammonia  excretion 
diminishes. 

Urea  is  an  inert  substance,  capable  of  uniting  with  acids  to 
form  unstable  >a!i>  (urea  nitrate  and  oxalate),  and  like  other 
amino  bodies,  being  decomposed  by  nitrous  acid  so  as  to  yield 
free  nitrogen  This  latter  reaction  is  used  for  the  ((uantitative 
estimation  of  urea,  the  evolved  nitrogen  being  proportioiml  to 
the  amount  of  urea,  thus : 

CO      +  2  UNO,  =  2. CO.  +  2  N,  +  2  ILO 

\ 
NIL 

(Vrtain  bacteria  are  capable  of  causing  urea  to  take  up  2  mole- 
cules of  water  so  as  to  form  aniiuouium  carbonate,  a  process 


no  I'llYHIOliOflY   FOR   PKNTAIi   STl'DKNTS. 

really  tlip  roverso  of  that  which  weun  in  the  orKanism  and  rep- 
rt'SiMited  by  the  above  forinul«>.  This  chanRe  oeeui-s  in  urine  a:i(l 
aeconnts  for  the  anunoniaeal  (nlor  which  develojw  when  thin  fluid 
Ih  allowed  to  stand. 

Creatinin.— This  is  very  clow-ly  related  to  creatin,  which  is  the 
most  abundant  extractive  substance  in  muscle,  and  which  yields 
urea  when  it  is  boiled  with  weak  alkali.  Thew  chemical  facts 
would  lead  us  to  expect  that  scmie  relationship  nm.st  exist  be- 
tween the  creatin  of  muscle  and  the  creatinin  and  urea  of  urine, 
but,  so  far,  it  has  been  impossible  to  show  what  this  relationship 
is.  One  very  important  fact  has.  however,  Iwen  brought  to  light, 
namely,  that  creatin  makes  its  appearance  in  the  urine  when 
carbohydrate  substances  are  not  being  oxidized  in  the  body,  as 
in  starvation,  and  in  the  disease  diabetes.  This  is  one  reason  for 
the  growing  belief  that  carbohydrates  are  something  more  than 
mere  energy  materials  (see  p.  li:}).  The  excretion  of  creatinin 
is  so  remarkably  independent  of  the  amount  of  i)rot«'i»i  in  the 
food  that  it  is  believed  to  represent  more  especially  the  end  prod- 
uct of  the  protein  break-down  of  the  ti.s.sues  themselves,  in  con- 
trast to  urea,  which  partly  represents  the  cast-off  nitrogen  of  the 
protein  of  the  food. 

PiRiN  HoDiES. — These  are  of  particular  interest  because  they 
include  uric  acid,  about  which  more  nonsen.se  has  been  written 
than  about  any  other  product  of  animal  metabolism.  The  so- 
called  uric  acid  diathesis  is  very  largely  a  medical  myth — a  cloak 
for  ignorance.  Trie  acid  is  the  end  oxidation  product  of  the 
I)urin  bodies,  which  include  the  hypoxanthin  and  xanthin  of 
muscle  and  their  amino  derivatives,  the  adenin  and  guanin  of 
nuclein. 

These  relationships  are  .seen  in  the  following  fornuilie : 

^  •        f  1  f  Hvpoxanthin CJl4N^0 

Oxv  punns  of  muscle }      •  *  ,  .  r,  it  xw^ 

'   ^  \  Xanthin   CJI^N^O, 

.        ,        ,  .        (  Adenin C5II4N4NH 

Amino  punns  of  nuclein . .  )  ^"'^"  "  r.  jt  ^r  rlx-tr 

(Guanin    C5H4N4OMI 

Uric  acid  CsH.N.O, 

There  are  therefore  two  sources  for  uric  acid  in  the  animal 


TIIK  MKTAHllMSM  <»F  I'ROTKINS. 


Ill 


bmly,  naiiu'ly.  th.-  inusolos  aiul  the  nudci  of  the  e.lls.  ThiH  ex- 
plains why  tin-  uric  acid  excretion  increnHcM  after  strenuous  mus- 
cular work.  an<l  wliy  it  is  nuich  above  the  normal  when  c-Uular 
l.reak-down  is  very  excessive,  as  in  the  <liseas.'  called  leucocythe- 
niia,  in  which  tlu-Ve  is  an  excess  of  leucocytes  in  the  blmnl  (8.-e 
p.  145).  Another  source  of  uric  acid  is  tlie  food  when  it  eon- 
tains  either  muwle  (flesh)  or  glands  (swe4-tbrea<ls).  for  a  lar^e 
proportion  (about  half)  of  the  iiiRested  purins  do  not  become 
destroyed  in  their  passage  through  the  organism,  but  become 
oxidized  to  uric  acid,  which  is  excreted  in  tlu;  urine.  This  is 
called  the  exogenous  in  contrast  to  purin  pro«luce«l  in  the  tissues, 
which  is  called  endogenous. 

There  is  only  a  trace  of  uric  acid  in  the  urine  of  mammals,  but 
in  birds  and  reptiles  most  of  the  nitrogen  is  pres.'nt  in  this  form. 
The  reason  is  that  in  these  animals  it  is  important  to  have  .semi- 
solid, instead  of  fluid  excreta,  so  that  the  urea  which  results  from 
l)rotein  metabolism  becomes  converted    into   uric    acid,    which, 
either  fr.H-  or  as  salts,  is  relatively  insoluble.    Trie  acid  is  chemi- 
cally a  diureide,  that  is  to  say.  it  consists  of  two  urea  molec»il.-s 
linked  together  by  a  chain  of  carbon  atoms.    The  chain  of  carbon 
atoms  is  furnished  by  substances  not  uidike  lactic  acid  and  the 
synthesis  occurs  in  the  liver.    If  this  organ  b."  removed  from  tlie 
circulation  in  birds,  sucli  as  geese,  in  which  the  operation  is 
comparatively  easy,  a  very  large  part  of  the  uric  acid  in  the  urine 
becomes  replaced  by  ammonium  lactate. 

The  relative  insolubility  of  uric  acid  and  its  salts,  which  we 
have  al"  referred  to,  makes  it  apt  to  become  precipitated  in 

urine.  •  ly  ou  standing.  It  forms  the  orange  reddish  de- 
posit, so  .erjuently  observed  in  summer,  when  on  account  of  per- 
spiration the  urine  does  not  contain  as  much  water  as  usual. 
Such  deposits  do  not  therefo'- ■  indicate  that  there  is  an  excess  of 
uric  acid  in  the  blood,  but  lUL.Ay  that  enough  water  is  not  being 
excreted  to  dissolve  the  usual  amount  of  urates.  Sonietimes  the 
urate  becomes  deposited  in  the  joint  cartilages,  particularly  in 
those  of  the  great  toe.  causing  local  swelling  and  redness  and 
great  pain.  This  is  gout,  and  it  may  be  most  effectually  treated 
by  drinking  large  quantities  of  alkaline  fluids,  and  eliminating 


112  l'IIV>I<>l,(NiV    KOH   t>H.NTM.   sTII>K,\TS. 

from  till'  (iiftary  s\icli  foudstiiirs  hs  mt-als  ami  sWfctbii'atlH.  wh'u'li 
yield  ('X<»Kiii(»u«  |>uriiis.  As  wi-  liavi'  saiil.  tlurc  is  no  reason  to 
iM'lifVf  tliat  any  otiitr  diseases  Insides  i^oiit  are  due  to  excess  of 
uric  acid  in  the  )il*H)d. 

Ilesides  the  above  there  are  traces  of  nllnr  iiitrot/t  mmx  siih- 
sttnirfs  in  tlie  urine,  such  as: 

1.  Hijipuric  acid,  whieli.  as  its  name  si^Miifies.  is  very  alnin- 
dnnt  in  the  urine  of  the  liorse  and  other  herhivora.  and  which  is 
the  excretory  product  of  the  aronuitic  sul»staiiees  whicli  the  fond 
of  these  ainiiials  contains. 

2.  Cystin.  an  amino  acid  containing  sulphur. 

:{.     I'i(;ments  and  inuciii. 

The  exact  si;iiiili(iitiii  iif  llu  rtiil  firoihu  Is  of  nilroiii  iioiis  mi  I- 
iiholism  has  heeii  very  lieautifully  demon.strated  liy  Folin.  of 
Harvard.  The  nbservations  vere  mad*'  on  several  men  who  lived 
for  .s'MMc  <iays  on  a  diet  ri<-h  in  piotcin  (hut  containing  no  jjurin- 
containin^r  f(M)dstu(fsl.  and  then  on  on(>  wliicli  was  very  poor  in 
protein.  The  ]H'ohlein  was  to  see  how  each  o'"  the  nitrdp-noiis 
constituents  Itehaved  duiinjr  the  two  periods,  both  absolutely 
and  in  relation  to  the  total  amount  of  idtroncii  "xcreted.  In  or- 
der to  sliow  the  latter  relationship  the  results  are  jrivcn,  as  in  the 
following;  table,  not  as  urea,  etc..  but  as  ureii-iiitro>rcn.  etc: 

On  tlif  protein-rich  On  the  protrlii- 

diet  poor  diet 

Quantity  of  urine 1170  c.  c.  385  c.  c. 

Total   nitrogen   16.8     gr.  :!.«  gr. 

Urea-nitrogen 14.7     gr.  (87  5)  2.2  gr.  (61.7) 

Ammonia-nitrogen 0.4!t  gr.  (:?.(•)  0,42  gr.  (11..!) 

Uric    acid-nitrogen    0.18  gr.  (1.1)  (».()!»  gr.  (2.r)) 

("reatininnitrogen (».58  gr.  (:!.6)  0.60  gr.  (17  2) 

Undetermined  nitrogen  ...  i>.85  gr.  (4.9)  0.27  gr.  (7.;!) 

Th(!  tij?urcs  in  i)arenthe.si's  repre.senl  the  jieie  ntatje  which  the 
nitrogen  of  eacii  substance  furnishes  of  the  total  amount  of  nitro- 
{ren  excreted.  It  will  be  seen  that  urea  decrea.ses  on  the  poor 
dirt  relatively  more  than  total  nitrDgio.  thus  indicating  that  it 
comes  partly  from  proteins  in  the  food  (exogenous)  and  partly 


TIIK   MKTM«H.I>M   i  »K   I'KUTKI.NS. 


1i:J 


fniiii  fill'  oru'iiiiiiHiit  it*l>'  (••rMlo«;<iiiiiis).     This  rrsiilt  Iih.N    • 
iiil'fi-  tliat  iiMwt  of  lilt'  iiiniiHi  MilisliiiircH  of  pnitfiii  Unt-  -U 

an-  not  rtM|iiiri'«|  an  hiiildinu  stfiiics  for  thi-  tisHiics  arc  fokni 
({own  so  as  toyicltl  ainiiioiiia.  wliii-h  is  cxcri'lt'd  as  .'xoKt'iioiis  una 
ill  tlu'  uriiii',  but  that  tlif  amino  l)o<lifS  that  aif  rnilly  appropri- 
iitcil  by  till'  tiMsufs.  ultliouKli  tbcy  may  also  pHHlm-f  soiii.-  iiri-a 
((•iiilotfi'iioiis"),  cause  other  eiul-produttH  to  be  formeil.  Thi-  iiionI 
im|>ortaiit  of  these  eiidojieiious  bodies  is  evidently  Cnitlinin,  for, 
as  will  be  seen  from  the  above  table,  this  substance  is  excreted  in 
the  same  absolute  amount  during'  both  the  starvation  and  the 
protein-rieh  periods. 

Direct  eviilence  t  .  t  this  conclusion  is  correct  has  been  ob- 
tained by  e\aiiiinatioii  of  the  blood  and  muscles  for  amino  botlies, 
ammonia  and  urea.  Tiie  results  have  shown  that  the  amino 
bodies  altsoibed  from  tlie  intestine  arc  carried  through  the  liver 
into  the  .systemic  blood,  which  transports  them  to  thi'  muscb'S, 
>  here  those  that  arc  not  recjuired  for  building  up  the  tissues 
arc  l)roken  down  into  ammonia  and  a  carbonaceous  residue,  which 
Is  then  burned  just  exactly  as  if  it  were  carbohytlrate  or  fat. 
The  ast'less  aniinonia  becomes  converted  into  urea  in  the  manner 
already  described,  either  in  the  muscles  themselves,  or  by  beinj; 
carried  to  the  liver,  which,  as  we  have  seen,  possesses  to  a  Very 
hi^h  decree  the  jjower  of  i)roduc'iiif;  urea. 

The  Relative  Importance  of  Proteins,  Pats  a  »<i  Carbci.y- 
drates  in  Metabolism. — The  metabolism  of  fats  i.   d  fi-fluilr. 
drati's,  with  rejiani  both  to  their  importance  a.s  buii   '  r,    •"  liwin,: 
tissues  and  the  tyi»e  of  tlioir  metabolism,  is  very  Ui:   tii  f.-c.n 
tliat  of  i)rotcins.     That  carbohydrates  and  fats  art  '  's  i'lipoi- 
tant  in  the  animal  economy  than  ])roteins  is  eviden«;.  i   h-    t' 
fact  that  we  can  live  jjcrfectly  well  on  protein  food  alv         Jui 
not  on  either  of  tlie  others.     This  docs  not,  however,  justify  us 
in  eoncludinp  that  carbohydrates  and  fats  are  merely  materials 
which  are  oxidized  by  tiic  ti.ssnes,  for  the  purpose  of  prcMlueiii'? 
encr}?y,  fuel  as  it  were,  and  which  can  be  dispensed  with.    They 
are  more  than  this,  for  no  cell,  in  however  starved  a  condition 
it  may  be,  is  entirely  free  from  either  of  them,  thus  indicating 
tliat  they  must  have  been  produced  out  of  protein  itself.     Pro- 


114 


l'llYSl(lI.O(iY    K()K    nKNT.U,    STinKNTS. 


I  . 


tciiis  ar.'  no  doiiht  the  mast  iiiii)oi't<iiit  in<;n'(1iciits  of  cflls,  Imt 
fills  and  carbolivdratcs  arc  iiidispcnsal)!!'  also. 

As  nstrn  tun  I  <  rials,  striking  diflVrcnccs  exist  l)ct\vt'<Mi  the 
llircf  foodstiifVs.  Protfiiis  arc  of  littl.'  value  in  this  regard  for.  as 
we  liave  seen,  very  little,  if  any.  can  beeonie  laid  down  in  tlie 
tissues  when  exeoss  is  taken  as  food:  on  tlie  contrary,  all  that  is 
not  re(|uired  is  thrown  out  of  the  body,  and  when  the  food  sup- 
jdy  is  cut  off,  as  in  starvation,  the  protein  is  spared  as  much  as 
|)ossible  (see  p.  !>2).  Carbohydrates  are  very  readily  depos- 
ited as  a  stareh-like  snl)stanee.  called  jjlycogen.  and  this  reserve 
is  tlie  first  to  l)e  called  on.  not  only  in  starvation,  l)ut  also  when 
muscular  work  is  perfornn'd.  It  nuiy  be  considered  as  the  most 
immediately  available  material  for  eond)Ustion  in  tlie  organism, 
but  the  limits  of  its  storage  are  restricted  in  man  to  some  hun- 
dreds of  grammes,  which,  as  we  have  .seen,  .soon  becomes  used 
lip  in  starvatioji.  Fat  is  i)re-eminently  the  .storage  material,  and 
the  supply  may  serve  in  man  to  furnish,  along  with  a  little  pro- 
tein, enough  fuel  for  several  weeks"  existence. 

The  relative  importance  of  the  tliree  foodstuiVs  is  shown  in  the 
extent  to  which  each  is  used  in  the  wdaholism  ilurinij  nuisnilnr 
/.rrrcisr.  When  tliere  is  an  abundant  store  of  glycogen,  the 
energy  is  entirely  derived  from  this  source:  when  there  is  little 
glycogen  but  mucli  fat.  it  is  fat  that  is  burned,  and  when  neither 
of  these  is  abundant  but  much  jirotein  is  being  taken  with  the 
food,  or  the  animal  is  reduced  to  living  on  its  own  tissues,  as  in 
starvation,  it  is  protein.  In  other  words,  the  type  of  metabolism 
occurring  during  muscular  work  is  the  same  as  that  which  imme- 
diately preceded  it ;  the  only  change  is  in  the  extent  of  the  com- 
bustion, not  in  the  nature  of  the  fuel  employed. 


ifisn 


CHAPTER  XII. 
SPECIAL  .METABOLISM   (ContM). 

Metabolism  of  Fats. — Fats  are  absorl)od  into  the  lacteals  and 
(list'liarged  into  tho  blood  of  the  left  subclavian  vein  through 
the  thoracic  duct.  They  arc  carried  to  various  i)arts  of  the  body 
and  gain  entry  into  the  cells,  in  the  i)rotoplasin  of  which  they 
become  deposited.  This  process  occurs  extensively  in  the  sub- 
cutaneous connective  tissues,  iH'tweeii  the  muscles,  and  retroperi- 
toneally  around  the  kidney  (the  suet).  The  fat  which  is  thus 
deposited  pos.sesses  more  or  less  tln^  .same  ((ualities  as  the  fat  of 
the  food.  Thus,  when  the  oidy  fat  taken  over  a  long  jx'riod  of 
time  is  one  with  a  very  low  melting-i)oint,  such  an  oil,  the  fat 
deposited  in  the  tis.sues  is  likely  to  be  oily  in  characti-r,  whereas 
it  is  stitl'  after  feeding  with  a  high  melting-point  fat,  .such  as 
nnitton  fat.  This  similarity  between  the  tissue  fat  and  that  of 
the  fiKHl  beconu's  very  striking  when  the  animal  has  been  sub- 
jected to  a  preliminai-y  i)eriod  of  starvation  and  then  fed  for 
some  weeks  with  a  large  excess  of  the  jiarticular  fat  and  as  little 
cai'bohydrate  and  i)rotein  as  possible.  Fat  in  the  IVmmI  is  of 
course  not  the  only  source  of  the  fat  in  the  tissues.  It  also  be- 
comes formed  out  of  carbohydi'ates,  a  fact  wiiieh  is  well  known 
to  farmers,  who  fatten  their  stock  by  feeding  them  with  maize 
and  other  starchy  grains,  and  to  i)hysicians,  who  reduce  their 
cor])ulent  patients  by  restricting  carbohydrate  foods.  The  fat 
thus  deposited  has  the  chemical  characteristics  of  the  fat  which 
is  peculiar  to  that  animal.  It  is  alinost  certain  that  there  is  ordi- 
narily no  formation  of  fat  out  of  protein  in  the  higher  animals. 

The  fat  thus  deposited  in  the  tissues  may  remain  for  a  long 
time,  but  ultin\ati'ly  it  is  again  taken  up  by  the  blood  and  car- 
ried to  whatever  active  tissue  rei|uires  it  as  fuel.  Before  being 
thus  burnt,  it  si)lits  into  glycerine  and  fat  acid  (see  j).  7.")).  Tlie 
fat  acid  possibly   undergoes  some  preliminary   change   in   the 

115 


ifrn^ 


116 


PHYSIOLOGY   POH   DKNTAL   STl'DENTS. 


'ivci';  ill  any  ciisc.  Ilic  loiijf  cliaiii  (if  ciirlHiii  atoms  of  which  we 
have  seen  fat  acid  iiiolcciiic  to  be  composed   (sec  p.  24,,  liccoiucs 
oxidized  (burnt),  not  all  at  once  but  iiiece  by  piece,  two  carbon 
atoms  beiiif,'  split  ofT  at  a  time.     If  the  fat  acid  chain  orijiinally 
contained    an    even    number    of    carbon    atoms,    the    oxidation 
process    may    stop    short    when    there    are    yet    four    carbon 
atoms     in     tlie     chain,     thus     producing     o.xybutryic      acid 
({.'II;,('II()II<'IL("()OII).     This  imperfect  metabolism  of  fat  oc- 
curs in  severe  cases  of  iliabetes  and  often  causes  death.     It  also 
occurs  in  carbohydrate  starvation,  and  indicates,  more  clearly 
than  any  thing  else,  tliat  even  caibohydrates  are  essential  for  life. 
Metabolism  of  Carbohydrates. — It  will  be  remembered  that 
these  include  the  starches  and  the  sugars,  and  that  during  diges- 
tion they  are  all  hydrolyzed  to  dextrose  or  hevulose,  as  which 
they  are  absorbed  into  the  blood  of  the  portal  vein.     This  ab- 
sorption is  rapid,  so  that  a  striking  increase  in  the  percentage 
of  sugar  occurs  in  the  blood  of  the  portal  vein  shortly  after  the 
food  has  been  taken.    :Most  of  this  excess  of  sugar  does  not  imme- 
diately gain  entry  to  the  blood  of  the  systemic  circulation,  how- 
ever, because  it  is  retained  by  the  liver.     For  this  purpose  the 
liver  cells  convert  the  sugar  into  the  starch-like  substance,  (jlyco- 
(jot,  which  becomes  deposited  in  their  protoplasm  as  irregular 
colloidal  mas.ses,  which  stain  with  iodine  and  carmine.    The  liver 
does  not  manage  in  this  way  to  remove  all  of  the  excess  of  sugar 
from  the  portal  blood,  so  that,  even  in  a  healthy  animal,  there 
is  a  distinct  postprandial  increase  of  sugar,  or  hyperglyciemia.  as 
it  is  called,  in  the  systemic  l)lood.    If  too  nuich  sugar  passes  the 
liver  it  causes  so  marked  a   postprandial  hyperglyca'mia  that 
some  sugar  escapes  into  the  uriiii'.  thus  causing  (jlycnsiiria,  which 
is  one  of  the  early  symptoms  of  diabetes,  and  whose  occurrence 
furnishes  us  with  a  warning  that  less  carbohv :     tes  should  be 
given  in  the  food.     If  the  warning  be  heedeu.  the  severer  foi-m 
of  the  disease  will  very  i)robably  be  staved  otY. 

The  glycogen  deposited  in  the  liver  stays  there  until  the  per- 
centage of  sugar  in  the  systemic  blood  begins  to  fall  below  its 
proper  level  (which  in  man  is  about  0.1  jier  cent),  when  it 
becomes  reconverted  into  sugar,  which  is  added  to  the  blood. 


THE  METABOLISM  OP  CARBOHYDRATES. 


117 


The  reason  why  the  sugar  in  the  systemio  bhwid  tends  to  fall  is 
that  the  tissues,  espeeially  the  nniseh's.  are  usiiip  it  up  as  fuel. 
If  so  mueh  sugar  is  taken  tliat  tlie  storage  eapaeity  of  the  liver 
is  overstepped,  the  e.veess  of  sugar  is  carried  Ity  the  .sy.stenne 
blood  to  the  tissues,  where  mueh  of  it  may  be  changed  into  fat. 
The  (jltfcogcnic  fiinctian  of  the  liver,  as  the  above  pnteess  is 
called,  is  analogous  to  the  stai'cli-forining  fuiuMion  of  inany 
plants,  such  as  potatoes,  of  the  sugar  which  is  formed  in  the 
green  leaves,  some  is  immediately  used  for  buihling  up  other 
substances,  the  remainder  being  converted  into  starch,  which  1m>- 
pomes  dei)osited  in  the  roots,  etc..  until  it  is  rccjuired  (as  during 
the  second  yeai''s  growth  i.  wiien  it  is  gradually  reconverted  into 
sugar. 

Besides  carboh.si rates  it  is  known  that  proteins  form  glyco- 
gen; fats,  however,  eaiuiot  form  it.  In  severe  caws  uf  diabetes 
it  is  therefore  usual  to  tind  that  althougli  earbohy<irate  foods 
are  entirely  withheld,  dextrose  continues  to  be  eliminated  in  the 
urine.  It  may  come  partly  from  the  protein  of  the  food  and 
partly  from  that  of  tlie  tissues. 

The  adjustment  between  the  I'ate  at  which  the  glycogen  of  the 
liver  beeonu's  eonvei-tcd  into  dextrose  anil  the  j>ei'ccntage  of 
sugar  in  the  systemic  blood  is  effecteil  partly  through  the  nervous 
system  and  partly  by  means  of  substances  called  chemical  mes- 
sengers or  hormones  (see  j).  124)  seci'eted  into  the  blood  from  tlie 
ductless  glands,  such  as  tln>  i>anereas  and  the  adrenals.  Tln' 
very  first  syvtptoms  of  <li(ihtt(s,  which  we  have  seen,  coirlst  in 
an  excessive  posti)ran(lial  rise  in  the  systemic  blood-sugar  and  a 
eonsecpieni  glyeasuria,  nui.st  tlieicfoi'e  l)e  due  to  defects  in  one 
or  other  of  these  regulatory  mechanisms,  so  that  it  is  of  great 
interest  to  know  that  glycosuria  can  be  induced  in  the  lower 
aninuds  by  stimulation  of  the  nerves  of  the  liver  or  by  interfer- 
ing with  the  function  of  the  pancivas  or  the  adrenal  glands.  The 
nerves  of  the  liver  nuiy  be  stii'inlated  either  direcHy  or  through 
a  nerve  center  located  in  the  iiedulla  oblongata  (see  p.  24()). 
Complete  removal  of  the  pancreas  is  followed  in  a  few  hours 
by  a  very  acute  form  of  diabetes,  which  is  invariably  fatal  in  a 
few  weeks,  whatever  the  treatment  nuiy  be.    Injection  of  extract 


■fr»r^f:^.  'r-^^  "  '^ierTs^s^?* 


118 


PIIYSIOLOflY   FOR   DENTAL   STUDENTS. 


of  the  adrenal  gland  (adrenalin)  causes  a  transient  hypersjlycie- 
niia  and  glycosuria. 

These  laboratory  discoveries  have  in    "  "ir  turn  caused  clinical 
investigators  to  pay  close  attention  to  tlie  vatiiir  of  the  causai 
of  diabetes.     It  has  been  found,  as  a  result,  that  oft-repeated 
overstimulation    of   tlie    nervous    system— nerve  strain,  as  it  is 
called— greatly  predisposes  to  this  disease.     For  example,  it  has 
been  found  that  a  considerable  proportion  of  students  who  un- 
derwent a  severe  examination  for  a  univei'sity  degree  had  glyco- 
suria in  the  urine,  wliich  was  i)assc(l  immediately  after  leaving 
the  examination  room.     Even  more  interesting  was  an  observa- 
tion on  the  urine  of  men  waiting  on  the  side  lines  as  reserves  in 
one  of  the  large  football  games;  about  one-half  of  them  pas.sed 
sugar,  due  to  nervous  excitation  of  the  glycogenic  function.    Be- 
sides thes<'  types  of  nerve  stiain.  nervous  glycosuria  may  also  be 
brought  on  by  fright  and  terror.     Tiiis  lias  perhaps  been  most 
definitely  shown  by  frightening  a  tom-cat  by  allowing  a  dog  to 
bark  at  it ;  tlie  cat  sliortly  afterward  passed  urine  containing 
much  sugar.     Now.  whereas  occasional  attacks  of  such  nervous 
glycosuria  are  harmless,  yet  their  ivpeated  occurrence  undoubt- 
edly weakens  the  ability  of  tiie  liver  properly  to  control  the  per- 
centage of  sugar  in  the  bloo<l,  with  the  coiise(iuen<'e  that  post- 
prandial hyperglyca>mia  becomes  more  and  more  marked  and 
takes  longer  to  disappear,  so  that  there  comes  to  be  a  permanent 
increase  in  the  percentage  of  sugar  in  the  blood.    This  persistent 
excess  of  sugar  acts  as  a  poison  and  causes  deterioration  of  many 
of  tiie  tissues,  and  if  unchecked  will  lead  to  severe  diabetr 
It   is  for  tliese   reasons  that  diabetes   is   relatively   c. 
amongst   locomotive   engineers   and   ship    captains;    it    is       -lo 
said  to  be  distinctly  on  the  increase  amongst  business  men.     A 
most  important  element  in  the  treatment  of  diabetes  is  tlierefore 
removal  of  the  possible  causes  of  nerve  strain.     Rest  and  M"i*'t 
and   freedom   from  worry,   cmii.le.l    with    removal   of  sufficient 
auKmnts  of  carbohydrates  fi'om  the  <liet   so  as  to  keep  tiie  urine 
free  of  sugar,  is  tlie  correct  treatment.     One  common  symptom 
of  diabetes  is  hmsening  of  the  teetii.    When  such  is  observed  tlie 
urine  passed  an  hour  or  so  after  lunch  siiould  be  examined  for 


TIIK    MKTAHOMSM   (»P   1N()R(!ANIC    SALTS. 


11!) 


su^jir.     Properly  poiuluctt'd  trcatinont  will  often  cause  the  teeth 
to  tighten  up  again. 

A  very  eoninion  eaiise  of  (h'atii  in  diabetes  is  eoma,  whieii  is 
due  to  the  poiso'iing  of  the  animal  liy  aeid  substances  (oxy- 
butyrie  aeid)  whieli  result  from  the  iniin-rfeet  oxidation  of  fat 
(see  p.  116).  While  these  aeid  substances  are  gradually  acciuuu- 
lating  in  the  blood,  the  organism  attempts  to  neutralize  them  by 
diverting  ammonia  from  its  normal  course  into  urea  (see  ]).  108)  : 
hence  the  ammonia  content  in  the  urine  is  very  high  in  severe 
ca.ses  of  diabetes.  Along  with  these  acids  and  anunonia.  acetone 
also  appears  in  the  urine  and  breath,  so  that  one  can  often  diag 
nose  a  severe  case  of  diabetes  by  the  smell  of  these  substances 
in  the  breath.  Diabetes  is  therefore  a  disease  which  the  denti.st 
should  always  be  on  the  look(mt  for. 

Metabolism  of  the  Inorganic  Salts.— Being  already  conj- 
pletely  oxidi/ed.  inorganic  salts  caiuiot  yield  any  energy  during 
their  pas.sage  through  the  animal  body  but  nevertheless  they  are 
essential  to  life.  They  are  used  not  oidy  for  the  building  up  of 
bones  and  teeth,  but  also  for  the  proper  carrying  out  of  the 
metabolic  processes.  In  this  regard  they  are  like  tiie  lubricant 
of  a  piece  of  machinery,  the  organic  foodstufTs  being  like  the  fuel. 

Their  indispensability  is  very  clearly  shown  by  the  fact  that 
animals  die  sooner  when  they  are  fed  on  food  from  which  all 
traces  of  inorganic  salts  have  been  extracted  than  when  they  are 
deprived  of  food  altogether.  This  result  shows  us  that  during 
the  metabolism  of  organic  foo<ls  .substances  must  be  pi'oduced 
which  act  as  poisons  in  the  ab.sence  of  inorganic  salts.  Some  of 
these  poisonous  substances  are  no  doubt  acid  in  reaction  because 
life  can  be  prolonged  for  some  time  by  merely  add'iig  sodimu 
cai'bonate  to  the  salt-free  fooil.  But  .salts  not  having  any 
neutralizing  powers  are  also  necessary  to  keep  the  animal 
alive. 

Till-  chief  salts  which  we  take  with  our  food  are  the  chlorides, 
carbonates  an<l  organic  acid  salts  (e.  g.,  citrates,  tartarates.  etc.) 
of  .swlium  and  potassium  and  of  caleinm.  \\\-  also  take  some  iron 
and  traces  of  iodine.  All  of  tlies<'  are  alreatly  i)resent  in  snfli- 
cient  amount  in  the  ordinary  foodstuffs,  excei)t  sodium  chloride, 


120 


PHYSIOLOGY   KOR   DENTAL   STUDENTS. 


J 


2U. 


or  common  salt.  Tliis  we  must  add  to  our  food.  The  extent  to 
which  the  addition  of  common  salt  is  made  varies  very  strikinsrly 
according  to  the  nature  of  the  organic  food  taken.  When  this 
is  mainly  vegetable  in  origin,  nuieh  common  salt  is  rcf|uired,  the 
reason  being  apparently  tliat  vegetables  contain  largo  (luantities 
of  potassium  salts  which  would  be  harmful  unless  a  proper  pro- 
portion of  .sodium  is  also  taken.  The  demand  for  sodium  by 
herbivorous  animals  often  inclines  these  to  wander  for  Inuidreds 
of  miles  from  '  eir  feeding  grounds  to  salt  licks.  Here  they  take 
enough  sodium  chloride  to  last  them  for  some  time.  The  carniv- 
orous animals  do  not  visit  salt  licks  uidess  it  be  for  the  puri»ose 
of  preying  on  the  herbivorous  visitors.  The  salt  hmtffrr  from 
which  they  suffer  compels  the  the  herbivora  to  the  salt  licks 
even  in  face  of  this  danger  of  destruction  by  the  earnivora.  Tlu- 
same  relation.ship  betv  eon  the  desire  for  salt  and  the  diet  is 
seen  in  man,  for  tiie  salt  consumption  per  capita  is  much  greater 
in  rural  communities  than  in  those  living  in  towns. 

I'sually  enough  iron  is  taken  either  in  meats  or  in  certain  vege- 
tables, as  spinach.  The  body  is  very  earefid  of  its  supply  of 
iron  (which  is  the  most  important  con.stitui'Mt  of  luemoglobin). 
but  if  it  loses  it  more  <iuiekly  than  the  loss  can  be  made  g(M)d 
from  the  food,  anemia  results  and  it  becomes  necessary  to  pre- 
scribe iron  salts  as  medicine. 

Similarly  with  cMlciiim,  there  is  usually  enough  in  the  food 
even  of  growing  animals  to  meet  the  demands  which  bone  and 
teeth  fornuition  entails.  Rickets  is  not  usually  due  to  a  defi- 
eicncy  of  calcium  in  the  food,  but  to  a  depraved  condition  of  the 
general  nutrition,  making  it  impossible  for  the  availabh'  ealcimn 
to  be  properly  used,  (iood  food,  air  and  exercise,  i-ather  than 
drugs,  is  the  correct  treatment  for  rickets. 

Our  knowledge  of  just  what  each  particular  inorganic  salt  does 
in  the  metabolism  of  an  animal  is  »iot  yet  very  far  developed,  but 
some  most  important  discoveries  have  been  made  in  this  connec- 
tion during  recent  years.  Thus,  by  obs.-rving  the  isolated  beat- 
ing heart  of  the  frog  or  turtle  it  !ias  In-en  found  thiit  a  certain 
l)roportion  of  sodium,  calcium  and  potassium  salts  is  essential 
■  to  the  maintenance  of  a  proper  beat.     With    so<lium    cidoride 


VITA  MINES. 


1_>1 


!i1(.M.-  tho  boat  soon  stops,  with  excess  of  potas-siuni  an  inunc.liat.' 
paralysis  ocenrs.  and  witli  excess  of  calcium  an  iniine.liate  rifior 
or  permanent  contraction.  Analogous  results  are  obtainetl  with 
other  muscles.  Salts  in  cci'tain  projiortions  may  ev(>ii  cause 
.j.roccsscs  of  ceil  division  to  start  in  tli.'  ova  of  sonn'  of  the  lower 
animals.  In  other  words,  a  process  of  .•mhryo  (h'velojjnn'nt  may 
whidi  is  usually  indued  by  impregnation  by  Die  male 
dements. 

Vitamines.     Tvpially  remarkabb'  as  adjinicts  of  diet  is  a  class 
of  bodies  calb'd  vitamines.     Without  tliem  metabolism  becomes 
upset,  and  serious  symptoms  make  their  ai.pearance  with  per- 
haps death  as  the  ultimate  r-snlt :  and  this  happens  even  altlioU','h 
the  protein,  fat,  carbohydrate  and  inorganic  salts  of  the  diet  be 
in  proper  proportion.     The  first  indication  of  the  imi)ortance 
of  vitamines  was  furnished  by  observations  on  a  disease  calleil 
liiri-liiri,  which  occurs  anion*,'  peoples  of  tropical  countri«'S.  and 
is  characterized  by  severe  neural<,'ie  pains,  muscular  weakness 
and  paralysis:  symi>toms  which  are  due  to  inflanunation  of  the 
ncrv.'S  (neuritis).    It  was  note.l  that  it  occurred  most  frequently 
in  the  cas((  of  people  whose  main  article  of  diet  was  polished 
rice,  but  was  infre(iuent   in  the  ease  of  tliose  usin^'  the  unpol- 
islied  grain.     The  difference  between  these  two  grades  of  rice 
is  that  the  on.-  (the  unpolished)  still  contains  .some  of  tho  brown- 
ish husk ;  the  otlier  is  free  of  it.     This  observation  suggested  tho 
experimont  of  adding  some  of  the  ground-up  rice  husks  to  tho 
polished  vice  diet  of  those  suffering  from  the  disease,  with  the 
result  that  the  symptoms  soon  disappeai-ed.     :Moreover,  when 
unpolished  rice  was  supplied,  in  place  of  polished  rice,  to  natives 
among  whom   l',eri-P.eri  was  very  prevalent,  the  disease  disap- 
peared entirely.    Other  foodstuff's  contain  this  vitamine,  so  that 
Beri-Bcri  does  not  occur  with  mixed  diets. 

In  order  to  learn  something  more  about  these  remarkable  sub- 
stances it  wa.s  necessary  to  seek  for  some  animal  in  which  .symp- 
toms similar  to  those  of  I'.eri-lh-ri  coidd  be  indii 1  by  feeding 

with  polished   I'ice.     Pigeons  were   foi  nd   most   suitable.      When 
these  birds  are  kept  exclusively  on  such  a  diet,  they  dcveloi>  the 


U'^ 


122 


PIIVSIOKOOY   FtiR   DENTAIi   STl'DENTS. 


most  alarming  symptoms  of  neuritis  (paralysis,  weakness,  etc.), 
which  however  disappear  in  a  few  houis.  not  only  when  unpol- 
ished riee  or  riee  polishinjrs  (or  husks)  are  given,  hut  also  when 
meat,  or  heans,  or  a  small  pie<'e  of  yeast  is  mixed  with  the  rice. 
Attempts  have  naturally  bi'en  made  to  isolate  the  substance 
which  is  responsible  for  this  i-emarkable  action,  and  indeed  some 
success  can  already  be  reported.  For  exampU".  it  lias  been  pos- 
sible to  separate  from  riee  polishings  and  from  yeast  snudl  traces 
of  crystalline  substances  having  a  most  powerful  action  in  pre- 
venting Jieuritis. 

Even  such  success  in  investigating  the  ca\ise  of  IJeri-Bcri  in 
rice-feeders  would  scarcely  warrant  us  in  asserting  that  vita- 
mines  are  essential  constituents  of  our  own  varied  diets.  To  show 
that  they  are.  however,  iias  been  mo  very  difficult  task.  Tiius,  it 
is  known  that  although  young  rats  thrive  admirably  on  milk  diet, 
they  fail  to  do  so  on  one  of  artificial  milk,  that  is.  of  milk  made 
in  the  laboratory  by  mixing  together,  in  proi)er  proportions,  the 
same  proteins,  fats,  carbohydrates  and  salts  that  occur  in  milk. 
In  this  chemical  mixture,  .something  is  wanting  wliich  exists  oidy 
when  the  ingredients  of  milk  are  compounded  by  the  mannnary 
glands.  The  addition  to  synthetic  milk  of  desiccated  milk  from 
which  most  of  the  proteins  had  been  removed  bestowed  on  it  full 
nutritive  value. 

The  practical  importance  of  this  observation  in  tlie  feeding  of 
infants,  we  lu'ed  not  insist  on.  Suffice  it  to  say  tiiat  it  is  quite 
po.ssible  that  i)rolonged  boiling  of  milk,  as  for  its  .sterilization, 
nuiy  deprive  it  of  vitamines  and  tlius  render  the  child  liaiile  to 
such  diseases  as  rickets  and  infantile  scurvy,  or  at  least  interfere 
materially  with  its  proper  development  and  growtii.  Among  the 
symptoms  th\is  ])roduced,  esi)ecially  in  the  ca.se  of  infautili! 
.scurvy,  ulcers  may  develop  on  the  gums,  or  the  teeth  may  become 
loaseneil.  Change  of  diet  may  in  a  few  days  restore  perfect 
health,  or  even  the  addition  of  a  few  teaspoonfuls  of  orange  or 
lemon  ,iuice  to  liie  original  diet  may  sutlice.  It  is  often  miracu- 
lous how  <|uiekly  such  ti'eatnient  may  change  a  fretful,  pain- 
stricken  ciiild  to  one  of  perfect  health  and  cheerfulness. 

InnuiuerabK'   other  exanipUs   uf   llie    wundirful    infiuciicc   of 


VITAMINKS. 


123 


tlu'se  nivHteriouH  vitniniii.'s  in  nutrition  nuKlit  l)e  fitt-d.  Tlif 
practieal  point  to  bear  in  n.iiul  is  that,  howcvor  convctly  our 
ilict  may  Iw  coniposwl  with  roRanl  to  calorie  and  ch.Mnical  r.M|unv- 
mcnts,  it  is  likely  to  W  unsviitable  unless  it  eoiitains  a  eertain, 
thouRh  perhaps  extremely  minut.".  amount  of  the  drug-like  sub- 
stance called  vitamines. 


i 


CHAPTER  XIII. 
THK  DL'CTLESS  (JLANDS. 

Introductory. — We  have  no  more  than  toiiclicd  Ihe  very 
l'iin(?e  of  the  subjeet  of  metabolism,  ami  yi-t  we  liavc  li-ariicd 
enough  to  imi)ress  us  with  the  faet  that  ..1th'  Utfli  it  is  extremely 
eomplieated,  it  is  ncvfrtlieh'ss  undt-r  pi-rftct  eontrol.  Jt  renuiiiis 
for  us  to  learn  soncthinK  regardinj?  the  nature  of  this  eontrol. 

If  we  take  sueh  a  metabolic  process  as  that  which  carbohy- 
drates undergo,  we  should  expect  that  the  conditions  which  deter- 
mine whether  glycogen  shall  be  formed  or  broken  down  would 
be  chemical  in  nature.  We  should  expect,  in  other  words,  that 
some  change  in  the  chemical  composition  of  the  blood — either  its 
reaction  or  the  amount  of  sugar  in  it,  or  the  appearance  in  it  of 
some  decomposition  product  of  sugar — woidd  determine  whetlier 
or  not  glycogen  .should  be  mobilized  a-s  sugar.  In  muscnlai-  work, 
fm-  example,  sugar  is  re(|uir(Hl  by  the  contracting  nniscles.  and 
we  find  that  the  gbcogen  stores  in  the  liver  become  very  quickly 
dei)leted  to  meet  the  denmnd.  The  (jue.stion  is,  how  do  the  mus- 
cles transmit  their  re(|uiremeiits  to  the  liver  so  as  to  cause  this 
organ  to  mobilize  the  dextro.se?  Our  natural  assumption  would 
be  that  the  active  muscles  cause  some  change  to  occui  "u  the 
blood  and  that  it  is  this  change  which  excites  the  liver  cells. 
Such  a  control  of  the  metabolic  activities  of  one  tissue  by  prod- 
ucts of  the  activity  of  another,  transmitted  between  them  In 
way  of  the  blood,  is  known  as  hormone  control.  We  have  already 
become  ac(iuainted  with  it  in  connection  with  the  control  of  cer- 
tain of  the  digestive  glands,  particularly  the  pancreas  (see 
p.  72),  and  it  is  no  doubt  very  largely  by  sueh  a  mechanism 
that  a  given  metabolic  i>rocess  becomes  active  or  supre.ssed,  as 
occasion  demands. 

The  hormones  in  sueli  eases  are  in  part  tiie  intermediary  \u-m\- 
nets  of  metabolism,  but  besides  these  hormones  others  must  exist 

124 


TIIK.  THYKOin  CI.ANO. 


125 


tt.  rail   fortli  •»!•  ivnnlatr  tlir  aclivitifs  of  tissihs  wliicli  arv  not 
iiniiir.liattiy  coiiciiu'd   in  ^r.•M»•l■al   ni.'tal.nliHni   Will    ratli.T  witli 
HiM'«-iul  proc'ssfs,  siH-h  as  tli."  i-Xfitubility  of  the  n.rvous  syst.-ni 
(»'.  >?.,  adivnalin").  tli.'  iM-havior  of  tli.-  ivpn)<l\i<-tiv.'  plaiuls  ( .-.  i?.. 
in  til."  s,M'ivtioii  of  milk),  tlu-  growth  of  cTtain  tissu.-s  (.-.  «..  of 
suhcutant'oiis  tissiu's.  of  hairs)  or  tlu'  atropliy  of  otli.Ts,  (c  ft.. 
of  the  uttTUs  aftt-r  piv^nancy  is  tt-rininati-d).     For  surli  lior 
nion.'s.  spt'cial  manufacturing  cfntn-s  arc  provi.l.-il  in  the  ilml- 
hss  ulaiuln.     The  thyroid  and  thymus  gUiuh  in  the  neck,  the 
pituitary  in  the  hrain,  the  spleen  and  adrenal  jrlands  in  the  ah- 
domen  are  kimkI  exi'iiiples.    None  of  these  has  any  duet,  hut  they 
discharge  the   pro.luets  of  their  activity— //(/' r/ir//   s<  en  lion— 
into  the  hloml  stream,  by  which  it  is  carried  to  the  tissue  or  organ 
on  which  it  acts.     Internal  secretions  may  also  l»e  produced  Ity 
certain  cells  of  the  diKcstive  jtlands,  as.  for  e.\aiMi)le.  the  si)-calletl 
Isles  of  J.annerhans  of  the  pancreas   (see  p.   12).  and  likewise 
there  are  certain  or^fuis  whose  main  functions  are  of  (|Uite  a 
special  natun-.  such  as  the  ovarii's  and  testes,  that  can  i)roduc.- 
very  i)Owerful  internal  secret  ions. 

We  shall  confine  our  attentions  for  the  i)resent,  however,  to 
the  strictly  ducth-ss  glands.  Their  function  is  ascertained  ex- 
perimentally either  by  removing  the  gland  by  oi)eration  or  by  in- 
jecting an  ixtract  of  it  and  then  observing  the  behavior  of  the 
animal.  Much  can  also  In-  learned  by  observing  i)atients  in  which 
the  gland  is  diseased. 

The  Thyroid  and  Parathyroid  Glands.— The  thyroid  gland 
consists  of  two  oval  lobes  situated  one  on  either  side  of  the 
trachea  just  below  the  larynx  or  voice  box.  and  eonne(  ted  to- 
gether over  the  trachea  by  an  isthmus  of  thyroid  tissue.  Km- 
bedded  in  the  substance  of  each  lobe  of  the  gland  on  the  i)o:stc- 
rior  surface  are  the  two  very  small  pamilujrukl  yhtmh.  :Minut<' 
examination  shows  the  thyroid  ghinds  to  h-  composed  of  vesicles 
lined  by  low  columnai-  epithelium  and  filled  with  a  clear  glo.s.sy 
substance  called  colloid.  The  parathyroids  have  an  entirely  dif- 
ferent structure,  being  composed  of  elongated  groups  of  poly- 
hedral cells  with  no  colloid  material. 

The  fuuctious  of  the  two  glands  are  probably  essenti.nlly  dif- 


126 


riiYsioi.iKiY  Kou  i»i:nt\i,  sti  dk.nts. 


f.'iviit.  \hv  tlivroi.l  liHvinjf  to  ilo  witli  the  ^f.-iu-ral  nutrition  of  tin- 
aninial,  iiml  tlic  |.ariitli,vioi.l  with  thr  n.ii.iition  of  tli.-  nnvoiis 
Kvstciii.  ThfV  li<'  so  (■h>sf  toK.-tli.T.  liowcv.  r.  that  it  is  v.-iy  ditli- 
cult  to  study  th«'ir  scparat.-  functions.  Th.-  iinportaiicf  of  tii.' 
Klnnds  is  indicated  by  the  relatively  large  hlmxl  supply. 


Fip.  10.— Cretin.  Ift  years  old.  The  treatment  with  tli.vrold  extract  was 
started  too  late  to  lie  of  benetil.      (Talient  of  I  >r.   S.  J.  Wel.ster.) 

"When  the  tiiyroid  is  not  properly  developed  in  children,  the 
condition  is  known  as  entiiiism  (Fif?.  10).  The  child  fails  to 
grow  in  height,  although  its  bones  may  thicken.  It  cranial  bones 
soon  fuse  together,  so  that  the  growth  of  the  brain  is  hindered 


Tin;   TliVKHll)   (il,\M). 


r. 


iithl  till-  iiii'iitiil  |M»\virs  r.iil  to  ilivilitp.  It  thus  h.coiius  iMiolir. 
:iiiil  iiltliiiimli  it  niiiv  live  lor  Vfjiis.  it  will  niiiiiiii  tvin  at  lliirt.v 
\<iifs  of  au<'.  ii  stiiiit.d.  |iot-lM'lluMl.  ii^l.v  mat  HIT  with  the  iiitil 
licence  of  an  infant.  The  cinisc  of  tliis  faiiiiiv  to  ij.'v.lop  in  uii- 
(loiihtftlly  hound  ii|>  in  noiim'  wa.v  witli  thf  ilcticicncy  of  tlif  thy- 
roid, for  if  thf  fntiii  hi'  >;ivtn  ixtract  of  this  kIiiikI.  itn  comiition 
will  iiiiiiitMliatfly  iiiiprovc,  ami  imli'iMJ.  if  tai<.n  early  enough,  it 
may  quickly  iiiaki-  up  for  lost  time  aiitl  yrow  hotli  phyHically  and 
iiii'iitally  as  it  ou^ht  to. 

Atrophy  of  the  thyroid  tfland  in  older  persons  causes  nii/rn- 
ill  mil      1  l*"i«.  lit.     The  syiiiptoins  of  this  arc  wvy  characteris- 


( Tigerstedt. ) 

tic.  lieiu^  iixist  coniiiionly  seen  in  women.  The  skin  is  dry 
and  often  of  a  yellowish  color,  the  hair  falls  out.  the  suhcutaueoiis 
tissues  yrow  excessively,  so  that  th(  hands,  the  feet  ainl  the  face 
become  large  and  j)un'y.  and  the  speech  indistinct.  Iiecause  of  the 
thickening'  of  the  lips.  The  nietaholism  .il-o  becomes  very  slu^;- 
flish,  so  that  the  intake  of  food  and  tl  e  \cretioii  of  nitrogen  in 
the  urine  become  diminislied,  and  tlie  teniperalurc  siibuormal.    If 


128 


IMIYSloLOiiY    KOU    UKNTAI.    STIDKNTS. 


li 


U  ' 


tit--     i 

t  ^ 


„„,,i...-k,..l.  n,..nl.l  syn.ptoM.s  Ium-omu.  Mpi.ania.  hrst  ol  ,  1  a 
,,inn.  o,-  th.  iut..ll....t  .1,1.  sl,..,.ln..ss  ana  '.■^'-•K>.  -^  ^^-; 
n,us..ulnr  twlt.-l.iM.s  and  t-vnors.     Just  as  m  '•"■^'   -" '^       ' 

X  to  disappear,  so  that  in  a  nn-ntl.  or  so  th.  patuM.t  luay  has  ■ 
r"tunu..l  to  his  or  her  uunnal  ..on.litlon,  to  nuuntau.  winch,  ho.- 
,.vor   tl...  thvroi.l  extract  must  continue  to  be  given. 

When  the", lan.l  is  removed  surgically,  either  m  lower  annnaK 
„r  in  nun.,  verv  aeut.  syn.pton.s  ending  in  death  usually  su.e,- 
"  ,        These  include  a  peculiar  form  of  muscular  tremor  cal    d 
:;,,  passing  into  actual  convulsions,  which,  by  .nvoWn.g  th 
respiitorv  >uusclcs.  ultimately  cause  dyspna-a  and  death 
is,  Loweve;.  probable  that  these  nervous  p-.nptoms  - ;^-      ^^ 
„  .avoidable  removal  of  the  parathyr...d  gland        Ihe  bt.i 
...oved  by  giving  -alciun.  salts.     T'''"-,  ^-'ij' ^y"     ' 
with  deficiency  of  the  thyroid  are  grouped  together  as  h>ji>oliu, 

"Ei^;;-in  healthy  individuals  thyroid  extract  taken  by  mouth 
..xeites  a  n.ore  active  metabolisn.,  and  may  cai.se  increased  lu . 
ac      itv      One  result  of  this  increased  metabolism  is  disappeai- 
.c    of  subcutaneous  fat  and  increased  appetite   thus  rendering 
Ur^^ninistration  of  moderate  doses  of  thyroid  ex^ra^ a  no 
uncommon  method  of  treatment   tor  obesity.     ^^  ^^^fT'^ 
should  never  be  attempted  except  under  ^^^^^^^^ ,^^f^^, 
eian,  for  it  is  very  .-asy  to  take  t..o  much  of  the  ext.act  and  (aus. 
iialnitation  and  lu'i'vous  excitement. 

'    Iv  en  the  thvroid   (and  parathyroid)   glands  become  exc-ss- 
iv^r    tive  in  imui.  the  condition  is  called  km>n-^U,roul..U  and 
:!-s;.,  ptoms  are  very  like  those  above  described  as  p roc  need 
;.  tiking  thyroid  extract.     To  be  exact,  tl.y  are  p.ilp    at    n 
wasting  of  the  muscles  an.l  conscMuent  weakness,  '-tu         . 
■ousneL  and  pr<,trusion  of  the  eyeballs.    On  "-"-^^^^  ^^ 
nK-ntioned  svmi,tom  the  condition  is  usually  called  ,xophlh„hnu 
;  Thi;  a  nte  and  often  fatal  disease  is  to  be  distinguished 

?    m"^,v,>uc  noUr.:,  in  which  there  are  very  few  gem-ra    symp- 
us,  but  greal  enlargement  of  the  thyroid  ^^^^^^^^ 
largJment  which  may  be  so  pronounced  as  practically  to  obUtci 


^<3^S^^ 


Tin;    ADUI.NAI.    (il.ANDS 


12t) 


Mti'  tilt'  neck  iiiid  siMiictiincs  so  compress  the  tniclicii  iis  to  iiitcr- 
fm"  witli  liri'iitliiii'r.  Tlic  cnscs  of  clironic  jroitn-  occur  in  tin- 
siiiiic  <listricts  ill  wliicii  tli<'  cxoiilitliiiiiiiic  variety  is  coiniiioii,  tlicsc 
iM'iiiK.  in  this  country,  the  shores  of  tlic  jircat  iiilaiul  lakes  ami 
the  river  valleys,  but  not  in  districts  hor.leriii'r  on  the  sea.  They 
are  also  coniiuon  in  certain  districts  in  Switzerland  and  Eii},'- 
land.  It  is  of  interest  that  in  the  lake  and  river  districts  in 
this  country  tlie  thyroids  of  over  ninety  pei-  cent  of  all  dojfs  are 
more  or  h'ss  hypi-rtrophied. 

The  aliDve  reniarkahle  iiiHueiice  of  tlie  thyroids  on  iiictaholisni 
is  in  .some  way  deiicndciit  upon  the  colloid  material  which  fills 
the  vesicles.  This  colloid  contains  a  peculiar  suttstance  called 
iodotliyrin.  because  it  contains  iodine,  an  element  which  is  not 
found  iireseiit  ill  any  other  i)art  of  the  animal  body. 

The  Adrenal  Glands. — As  their  name  sifinifics,  these  arc  .situ- 
ated one  oil  cither  side  just  above  the  kidneys.     Each  gland  is 
yellowish  ill  color,  and  is  seen  on  microscopic  cxaiiiinatioii  to  be 
composed  of  a  medullary  and  a  corticiil   portion.     The  medulla 
consists  of  irrefrular  collections    of    cells    containing    granules 
which  stain  decitly  brown  with  chronic  acid  and  are  therefore 
called  chromophile  granules.    Similar  chromophile  granules  may 
exist   in  other  parts  of  tli<'  body.     The  great  splanchnic  nerv<', 
which  it  will  be  remembered  arises  from  the  sympathetic  chain 
ill  the  thorax  (sec  p.  27M).  makes  very  intimate  connection  with 
the  adrenal  medulla,  for  which  i-easoii  and  because  of  the  fact 
that  it  is  developed  from  the  same  embryonic  tissue  as  the  sym- 
patlietic  system  of  nerves,  the  medulla  of  the  adrenal  gland  is 
believed  to  be  closely  bound  up  with  the  functions  of  the  symi)a- 
tlietie  nervous  system.     The  cortex  is  composed  of  rows  of  col 
uiijnar  cells  which  do  not  contain  chromophile  granules.     Small 
though  they  be,  the  adrenal  glands  are  es.seiitial  to  life,  for  their 
removal  causes  extreme  muscular  weakness  and  a  fall  in  blood 
pressure  followed  by  (h'atli  within  twenty-four  hours.     When 
they  are  the  seat  of  di.seaso  (tubercular),  symptoms  of  extreme 
muscular  jirostratiou.  accomitanicd  by  vomiting  and  a  peculiar 
bronzing  of  the  skin,  set  in  and  grow  steadily  worse  until  at  last 
the  patient  succumbs.    This  is  called  Addison's  disease. 


i:U) 


I-IIVSI(IMH;Y    for    OKXTAr,    STIOKNTS. 


The  most  striking  proof  of  tlu-ir  iiiiportanco  is  .>l)taiiu'<l  by  iii- 
.i..ctinfr  an  extract  of  tl.c  m.-dulla  ..f  the  a.hvnal  ^\:uu\  ...to  a 

'vein      It  causes  an  imi Hate  rise  ...  l.U.o.l  p.vssiire.  wliiel.  is 

more  or  less  propoi-^ional  to  the  st.vn-1h  of  th.'  ."xti-act.  The 
rise  is  aceon.paniea  by  a  shnving  of  the  h.-a.'t,  .l.ie  to  the  reflex 
stimulation  of  the  vagus  eeut.-e  excited  by  the  rising  bloo.l  pres- 
sure When  this  reflex  slowing  is  rendered  impossible  by  cutting 
the  va.'i.  the  rise  in  bl.Kul  j.ivssn.v  following  the  injection  may 
i„.  enormous.  The  active  substance  in  the  extract  is  called  min  n- 
alin.  sui>r,m>,i>,,  mlroin  or  rpinrphri,,.  It  is  a  eompa.'atively 
simple  chemical  body,  having  the  formula ; 

(11 

(II())('  iClKIIiOlIjriL  — MICH, 

(1I())C  iCII 

(•II 

and  .-xisting  in  two  vari.'ties  which  diffe."  from  one  another  ae- 
coi'ding  to  the  din-ction  to  which  the  plane  of  polarized  light  is 
rotated.  The  vai'iety  rotating  to  the  left  is.  by  many  t.nies. 
stronger  in  its  physiological  actions  than  that  which  rotates  to 
the  right.  The  discovery  of  its  eh.'mical  structure  has  made  it 
l)ossible  for  chemists  to  prepare  suj.rarenin  synthetically,  and 
al«o  to  prepare  a  ser.es  of  ivlated  substances  having  less  n.arked 
l.roperties  of  a  similar  kind.  These  are  closely  r..late<l  to  certain 
of  the  bodies  which  appear  during  the  putrefaction  of  meat. 

By  careful  studies  of  the  action  of  the  supraivnin.  or  related 
substances,  it  has  been  found  that  the  rise  i..  bloo.l  pressure,  above 
referred  to,  is  due  to  stimulation  of  the  mu.sde  fibers  in  the  walls 
of  the  blood  ves.sels.  It  is  on  this  account  that  a  weak  solution  of 
suprareiiin  is  used  to  stop  ha-morrliage.  as  after  removing  polypi 
from  the  nose,  or  in  bleeding  from  the  gums,  as  after  tooth  .'X- 
traction.  The  muscle  of  arteries  is  by  no  means  the  only  struc- 
ture on  which  adrenalin  acts;  indeed  it  stimulates  every  .structure 
which  is  capable  of  being  stimulated  by  the  sympathetic  nervous 
system  (see  p.  277).     Thus,  it  causes  the  pupil  to  dilate,  saliva 


TllK  I'lTI  IT.\I{Y  OLAND. 


i:u 


to  hv  scented  (p.  41  ).  the  movements  of  the  inte-tine  to  be  in- 
hibited (]).  7!li.  whereas  it  luis  no  aetion  on  tlie  blood  vessels 
ol'  the  hnifirs  or  brain,  which  do  not  jtossess  vasomotor  nerves. 
This  similarity  Ix'twecn  the  results  wiiich  iVtllow  suprarciuri  in- 
jection and  stimnlation  of  the  sympathetic  system  is  parfieiilarly 
siirnitieant  when  we  call  to  mind  the  fact  that  tlie  medulla  of  the 
adrenal  ^land  is  developed  from  the  same  embryonic  tissue  as 
the  sympathetic  system.  The  dottinir  power  of  the  blood  is 
diminished  after  injections  of  snpi-areiiin. 

The  Pituitary  Gland.— Tins  occupies  the  Sella  Turcica  of  the 
base  of  the  cranium  and  is  eomi)osed  of  three  jiortions  or  lobes. 
The  anteri(.r  lobe  consists  of  larjre  epithelial  cells  and  is  really 
an  isolated  out^'rowth  from  the  epihlast  of  the  upper  end  of  the 
alimentary  canal.  Its  com])lete  excision  causes  death  in  a  tew 
days,  but  if  only  a  part  is  I'emoved.  a  condition  called  In/po- 
pititit(iri.s)n  develops,  of  whicii  adijiosity  and  sexual  impotence 
are  the  main  ,symi»toms.  When  this  lobe  becomes  excessively 
active  in  man  (because  of  hypertrophy),  it  causes  a  peculiar 
growth  of  the  bones.  i)articularly  of  the  lower  jaw,  thus  making 
the  person  look  as  if  he  were  vei-y  powerful.  This  disease  is 
called  (icromrffdhj  (Fi^'.  12).  and  besides  the  dianges  in  the 
bones,  there  is  frequently  considei'able  metabolic  <listurbance, 
causinjr  a  mild  form  of  diabetes.  When  the  hypertrophy  of  the 
anterio:-  lobe  occurs  in  youth,  most  of  the  bones  of  the  body  may 
bo  atfected,  thus  causinjj  the  condition  known  as  ijiiutlisw. 

The  intermediary  lobe  is  also  comixjsed  of  colinnns  of  epithe- 
lial cells,  but  there  is  often  some  colloidal  nmterial  between  the 
columns.  This  colloid  ditfers  from  that  of  the  thyroid  in  con- 
taining im  iodine. 

The  i)osterior  lobe  is  I'eally  a  down^'rowtli  from  the  brain,  and 
is  compo.sed  of  neuroglia  mixed  with  some  of  the  epithelial  cells 
of  the  intermediary  lobe.  This  lobi'  can  be  excised  without  caus- 
ing any  evident  change  in  the  animal,  but  nevertheless  it  must 
have  some  important  functions  to  jxrform.  because  extracts  of  it. 
when  injected  intravenously,  have  very  i)ronounced  effects,  vi/. : 
(1)  a  rise  in  blood  pressure:  (2)  a  very  striking  diuretic  action 
(i.  e.,  causes  urine  to  be  excreted)  ;  (3)  secretion  of  milk.     The 


\:\2 


IM 


1VS1()1.0(!Y    FOR    nr.NTAI,    STIOKNTS 


a.tivo  pri.u-iplo  of  th.-s..  .xtra.-ls  has  not  as  y.t  b.-e.i  isolate.!. 
„lth..v.«l.  tin-  extracts  can  lu-  .-onsMcrably  concent ratcl,  thus 
vi.'hlinir  tlic  tnuh'  preparation  called  pihnlnn. 
■  It  is  particularly  inten-stin;:  to  note  that  altlum^-h  the  anter.or 
lobe  does  not  yiel.l  any  active  extra<-t.  yet  its  exc.sn.n  .s  atal. 
,>„  the  other  hand,  the  posterior  lobe  can  be  removed  with  un- 
punitv.  althouRh  .-xtracts  of  it  have  profoun.l  physioloK.cal 
,,tf,.i.ts  when  they  are  injected  into  normal  animals. 


■DiiifBiilis  symp- 
Aflei 


KiK  U  -A.  To  s.,..w  th..  appeKrano..  Uefo.v  the  onset  ..t  "-^r,u-^.U.  .: 
„.,U  «.  T.,..  ..ppearan...  aft.-r  .ev.ntoen  years  of  ...e  disease.  (. 
CiimpbeU    (ieddes. ) 

The  Spleen.-Notwithstandintr  the  fact  that  this  is  the  larg- 
est of  the  ductless  glands,  it  is  the  one  whos,-  functions  are  the 
least  well  und.'rsto.xl.  It  can  be  ex.ise.l  without  causing  any 
.videiit  disturbance,  an.l  extracts  of  it  when  injected  mtraven- 
ouslv  do  not  have  any  characteristic  etTects.  It  beconu.s  wry 
much  enlarge,!  in  certain  .liseases.  namely:  (D  n.  leucocythe- 
„na.  a  form  of  aiuemia,  which  is  characterized  by  a  great  increase 
in  the  leuco<-ytes  of  the  blood  (see  p.  145)  ;  (2)  in  typhoid  U^vv 
(enteric  fevc-r)  :   (3)   in  malaria.     It  becomes  contracted  after 


TIIK  TIlVMrs  til. AM). 


i:{:{ 


liikiiifj  i|uiiiiii('.  T'mlcr  tlic  niieroscoix'  it  is  seen  to  he  (•(iiiipiisiMJ 
of  a  spoil",'!'  of  fibrous  tissue,  tlic  sfmccs  iM'injr  tiili'd  witli  blood, 
whicli  flows  frt'fiy  into  them  from  artcriolfs  in  wliosc  walls 
lyiiiplioid  tissue  is  abundant.  Here  and  liiere.  tiiis  lymphoid 
tissue  l)eeomes  collected  in  nodules,  wliieli  are  larp'  eiioujili  to 
be  .seen  l)y  tlie  naked  eye  and  are  called  .Malpijrhiaii  corpuscles. 

In  tlie  blocul  of  the  spleen,  partly  broken  down  erythrocytes 
are  often  visible.  Soinctimes.  also,  cells  like  those  found  in  red 
bone  marrow  and  having;  to  do  with  the  manufacture  of  new  red 
corpuscles  make  their  api)earance. 

Taking  all  these  facts  togethi'r,  it  is  believed  that  the  spleen 
has  the  following  functions:  (1)  manufacture  of  leucocytes; 
(2)  inamifacture  of  erythrocytes;  (;5)  destruction  of  erythro- 
cytes;  (4)   removal   from  the  blood  of  certain  poisons. 

The  Thymus  Gland. — The  thymus  gland,  situated  at  the  root 
of  the  neck,  is  (|uite  large  at  birth,  but  its  si/e  gradually  dimin- 
ishes as  the  animal  grows.  I>y  the  time  that  puberty  is  reached, 
it  has  almost  di.sappeared.  It  is  composed  of  peculiarly  arranged 
lymphoid  ti.ssuo,  having  nt'sts  of  epithelial  cells  embedded  in  it. 
It  .seems  to  bear  some  relationship  to  the  generative  glands,  for 
its  removal  in  young  male  animals  hastens  the  growth  of  the 
testes. 


1 


n 


Vm 


(IIAPTKH  XIV. 

ANLMAI.  HEAT  AND  FEVEU. 

1„  c-onsLl.Tin^  tlu-  ,.n.bl.-n,  of  aninw.l  iu-at.  it  is  .ss.ntial  t-. 
,„,,r  c-lcarlv  in  nu.ul  th.  .listinctiou  In-tw.-.M.  anu.unt  a.ul  int..  - 
sitv  of  heat.     Tlu-  for.nn-  is  nu-asun-l  in  caloru-s   (s.-.  p.  K4  , 

,,  ,,  ,  „,a„  a  n.axin.al  tiu.rn.oMu.t.-  w.th  the  ^>^^ 
.r  V.ut\^VH,W  seal.,  is  placul  in  soni.  prot.-.-t.-a  part  of  ti.e  l.o.l>. 
as  the  mouth,  the  axiUa  or  the  .v.-tun..     It  is  foun.l  by  suc-h  n.eas 
„,,nH.nt  that  the  tenu-rature  varies  aeeor.l,n«  to  the  s.t^e  oi  ob- 
servation  an.l   the   tin.e   ..f   day.      It    vanes   between   .{b.O^    (  . 
(%8^'  V  )  ar-.l  :n.8    C  (100.0    K.  i  in  th.-  reetuni;  l.etween  .i(,..5 
(•    ;!,73'  F.)  and  :{T.5    C.  {^^    F.)  in  the  axilla;  ami  between 
:J6  '  C'  (96.8^  F.)  an.1  :n.25    C.  (!H).:r  F.;  in  the  mouth.    These 
variations  in.lieate  that  the  ten.perature  is  higher  ,n  tl^'  deeper 
than  in  the  snpertieial  parts  of  the  body;  ^n  other  wonls H  at 
t,H.  visceral  blood  is  warn.er  tl>an  tiu.t  of  the  snrtaee  ot  the  bod> 
The  variations  of  ten.perature.  due  to  the  tune  ot  day    are  n.ost 
evident  when  it  is  taken  in  the  reetnn..  and  they  anumn    m  health 
,.,  ,  Httle  ov..r  1     C  or  a  little  below  2     F..  the  h.ghest  ten.pe.  ^ 
ture  oceurri),g  about  :?  p.  m..  an.l  the  lowest  about  3  a.  m.    This 
is  called  the  iUurnol  rarialion  an.l  it  n.ay  b.-.-om.-  ...u.-l,  ^tvat.-i 

in  febrile  diseast^s.  i    i    ..^> 

Anin.als  whos.-  ten.p.-rature  b.-haves  as  above  described  are 
called   warm-bloodai  in  contrast  to  ..ther  anm.als.  .-alh-.l  ro/.  - 
l^loodecl,  in  wh.>m  it  is  only  a  d..gree  ..r  two  above    hat  ot    1 . 
air   with  which  it  runs  parallel.     Such  annuals  n.clu.l..  hsl  •  s 
an.phibians.  snak.-s,  etc.    U.^w.-en  the  eol.l  an.l  the  warm-bloo.  ed 
ani  nals  is  a  gr.mp  in  whi.-h  the  aninud  is  warm-blo..de,l  nt  sum- 
;;::  an.l  col.l  bl.>o.l.-,l  in  winter.     These  are  tl...  Jul.  r.aln,,  'on- 
,„„ls,  such  as  the  luMl«eh.>j;,  the  marmot,  th.-  bat.  et.-.     In  tins 
coni-ectiou  it  is  interesting  to  note  that  th.>  human  u.fant  be- 

134 


AXIMAI-    IIKAT    AND    FIAT.U. 


i:?.') 


hav.'s  more  or  Irss  lik.'  a  cold-hlofxlcl  aiiiiii.il  for  some  time  ini- 
in.'diatcly  following  birtli.  .luiin«  wliicli  jH-riod  it  must  tlu-n-- 
fore  be  carefully  protected  from  cooling',  for.  if  its  temperature 
he  allowed  to  fidl  to  any  considerable  extent,  it  is  not  likely  to 
survive.  It  tak.'s  sev.'ral  moiitlis  before  the  heat  rejmlatin>; 
mechanism  bec(mies  so  .leveloped  that  the  infant  can  withstand 
anv  considerable  dejrree  of  cold. 

Factors  Concerned  in  Maintaining  the  Body  Temperature.— 
The  body  temi)erature  is  a  balance  between  heat  production  and 
heat  loss.     Heat  is  prixhical  by  combustion  of  the  orjranic  food- 
stuffs in  the  muscles,  the  amoun    which  each  foodstutf  thus  pro- 
duces being  the  same  as  when        is  burne<l  outsith-  the  Ixuly. 
except  in  t)ie  case  of  i>rotein.  where  allowance  must  be  made  for 
the  incomplete  condaistion  of  this  substance  in  the  animal  body 
(see  1).  S.">).     The  nuisdes  are  tli<-refore  the  furnaces  of  the  ani- 
mal body,  the  fuel  bein}?  the  organic  foodstuffs.     Heat    is  lost 
from  the  body  nnvwW  from  the  skin,  but  partly  also  fi'om  the 
lungs  and  in  excreta.     Heat  loss  from  the  skin  is  brought  abmit 
by  the  utilization  of  several  physical  proces.ses,  namely:   (1)  by 
conduction  along  objects  which  are  in  contact  with  the  skin  ()r 
through  the  air;    (2)    by  convei-tion.  that   is.  by   being  carried 
away  in  currents  of  air  which  move  about  the  body;  (M)  by  radi- 
atioii;   (4)  by  evaporation  of  sweat.     This  last  is  the  means  by 
which  most  heat  can  be  lo.st.  because  it  takes  a  large  amount  of 
latent  heat  to  vai)ori/.e  the  sweat  (see  p.  20). 

Heat  loss  from  the  lungs  is  mainly  due  to  vaporization  of 
water,  with  which  the  exi)ired  air  is  saturated.  .\  small  anu)unt 
is  also  alworbed  in  warming  the  air  itself.  The  heat  lost  in  the 
urine  and  fu'ces  is  almost  negligible. 

The  Regulation  of  the  Body  Temperature.— It  is  i)lain  that 
a  very  .sensitive  rcgiilatory  mt-ehanism  must  exist  in  order  that 
the  production  and  loss  of  lieat  may  be  so  ad.justed  as  to  keep  the 
body  tempi-ratur.'  practically  constant.  When  lieat  loss  becomes 
excessive,  then  must  heat  i)ro(luetion  be  increased  to  imiintain  the 
balance,  and  rln  n  rso  when  heat  loss  is  slight.  The  conditions 
are  to  a  certain  extent  comparable  with  those  obtaining  in  a 
house  heated  bv  a  furnace  and  railiator.s  and  provided  with  a 


i:!(; 


I'llYMOl.d'.V     KOK    DKATAl.    STIOKNTS. 


t,...,,„o-r..Kulator.  wln.lu  lu-in,  a.-tivat.-.l  l-y  U.-U-unu-vMnv.  of 
tlu-  n.oins.  acts  ....  tlu-  fuma.M-  s.,  as  to  ....s.-  ...■  I..vv.t  .ts  ,at..  ut 

1„  tl..-  a..imal  l.o.lv  tl.-  1lu..-...o-.v-ulato.-  ,s  tl..  ur^um.  s  s- 
t..,„      \Vl.H..-v.'.-  11..'  t.i..iM..'atu.v  of  tl..  I.I00.I  .-haop's  l.-oin  tl..- 
„„,;„,,.  .  ......v..  ......tn.  .-all..!  tl..-  //nmo,,./..  l..-o,„.-s  a.-t.-,    on 

with  tl..-  .vs..lt  that  it  t,-a..s...i1s  i>,.imls,-s  t..  tl..-  .....s.-h-s.  Nvh..li. 

,,,   i„,n.asi..^'  ..r  .lin.inishi.,n  th.-i.-  to...-    (s.-.-   ,.2..:$..  .-aos..  a 
./n-at.-r  or  a  h-ss  h.-at-i..-o.lu.-ti.>...    I'-.t  th-  .-.-..t.v  . lo.-s  umv  tl.a.. 
^l...  th..rn,o.r.-jj,.lato..  of  a  l.o,.s...  f...-  it  .•.mt.-..ls  th-  a,.-...-..-s  ot 
h.-at-loss      Thus.  wl..-..  tl..-  I.I00.I  t,-...p.-rat,..v  t.-...ls  t..  r.s.-.  tl..- 
t„..,„H>,....i.-  c..-..t.-.-  -aUM-s  .....n-  h..at  t.=  1..-  Inst  f......  th.-  sk...  a... 

,,„.,.  i,.  tl...  followi..,'  ways :     (1  .  It  a.-ts  o..  th-  h  00.    v.-ss.  s  ,  f 
,h..  ski...  .....sin,  th-,..  to  .lilat..  so  that  ...on-  hlo.-l  .s  hr..u,ht  t 

th..  s,.rfac--  of  th-  h...ly  to  1.-  ..x.l-.l  otT.  (2)  It  .-x.-.t.-s  th-  ,s«-at 
.lan.ls.  so  that  ...o.-.-  h.-at  has  to  h.-  ,.tili/,.-.l  t..  .-vaporat.-  th.-  sw.-at. 
(15)  It  .ii.i.-k-ns  th.-  n-spiratio-.s.  so  that  ...o.v  a..-  has  t..  l..- 
wan...-.l  a..a  saturat-.l  with  n.ois,.,,--.  Th.-  .l-.n-.-  to  wh.-h  th.s- 
,.,„,i„^  pm-SH-s  a.-.-  ,.s.-.l  va.-i-s  i..  .iitV-n-..t  a...n.als  lh,.s 
the  dojj.  si,.-  th-,v  an-  ..o  svv.-al  ^'la„.is  ov.-,-  th-  su.-ta-.-  ot  h. 
iKxlv  (th-v  ar-  -oi.fi.UMl  to  th.-  na.ls  ..f  th-  paws),  .„.-n-as.-  .„  th.- 
,-..spi,-atiou   is  th.    chi-f  ,...-tho.l  ..f  -ooli,.«.   l.-> tl..-   pa..ti,.^' 

0,1  warm  .lays.  ;  ,   ti  . 

1„  th.-  -as,>  of  ,..a>..  civili/ati..,.  has  st-pp.-l  .„  to  ass.st   t  „ 
,vt1.-x  -o,.t,-ol  of  h-at  loss,  as  by  th.-  .-hoi.-.-  of  H.-thn,,'  a,..i  th- 
artiti-ial    h-ati..^  of    .•oo„.s.      D-si.-ahh-   tl...u..h    th.s   vol,„.ta,-y 
......trol  of  h-at-l«ss  f,-.„..  th.-  h...ly  -aay  h.-.  tl-,v  -a,,  h-  1>     *• 

.lo.iht  that  it  is  oft.-.,  ov-nl..,.-  to  th-  .l.-t,-n.,-..t  ot  «oo<l  h-alth. 
Livi,..'  i..   ov.-rh.-at...t    .•m.„.s  .l..ri..!Z   th.-   .-ool.-r  .„o,.ths  ot    th.- 
v-ar  r,.pp.vss.-s  to  a  v.-ry  low  .h-.n-.-.-  th-  h-at  h>ss  f.-.m.  th-  hody 
in,.!  th-n-hv  1..W.-.-S  th-  to..-  a,..l  h.-at  pn..l,.-tio,.  of  th-  ,.,us-,.lar 
svst-n,      Th-  foo.i   is  th.-n-hy   i..-..„.pl.-t.-ly   ,..-tal...l,/.-.l  a,..l   ,s 
stored  away  as  fat  ;  th-  s„p..,-fi-ial  .-ai.iUa.-i.-s  a,-.-  ......stn.^.-.l  a... 

th-  ski..  h.-c-..,.i-s  l.loo,ll-ss.  r.ut  it  is  ,.ot  l..oks  alo,,.-  that  snt  .-  , 
b.,t  h..alth.as  w.-U,  fo.-.  hy  havi..^'  s.,  littl-  1..  .lo.  ti„-  h.-at-,v-u  at- 
\uyr  ,...-ha,.is„.  n-ts  out  of  f..-ar  so  that  wl.-..  it  ,s  .--..u.,--.!  o 
a.;  as  wh-,1  Ih-  p-rson  go.,  uutsitl-.  it  .nay  ,.„t  do  so  p,-o,.,ptly 


AMMM.     in;\l'    AM'    KIAI.U. 


VM 


wliat.  ana  ..ata.Tl.s...t.-..  an.  tlH., vM.lt.  TI....V  ..an  h.  h,t  ,■  .1,.,.  t 
that  nuM-h  of  tl„.  l..-n..tit  nf  .M-'M-air  sl....,..n^  ,s  .  n.  "'  1'-  ;'  - 
stant  stinn.lation  of  th-    n.-tal-.h,.    ,.r ss-s    wln.-l.    .t    h,.n>;s 

"'"It  iniiM.rtan...  nl-  ,1..  ,.va,M..alion  nl' su..at   in  l.rin^in^  alM 

,.,s.s  ..f  h..at   in  nnn.  partly  .xplains  wl,v  ,ll.,al,    sln.nM  In.v.  su 
.„„,,„„,„  inHu.n....  nn  l.is  w,.ll-l...inv'.     it  is  ..ut  s.,  nu,..!.  tlw 

,.,,;,,,,,,,,,  ..Ml.,  air.  as  its  n.lativ..  Innniai.y.  lliat  .s  n    u.M.".- 
„„,',,  that  is.  tl...  .h.,Mv...  ..M.n.ss,..!  i..  p..m.nta,.-.  K.  whu-h  th. 

.,n-  issatnn.t...l  with  n.nistnn.  at  th.  t,.>n|nTatn.v  ot  „l.s..rvatmn 
Thus,  a  ivlativ..  h.nnnlitv  of  T-".  l-.-r  .-nt  at    L".     C  n.-ans    hat 
th.  air  .Mmtains  T-'.  p.r  ....nt  of  tl...  total  anu.unt  of  n.o.stur..  xvh..-l. 

it  w.ul.l  .-ontain  if  it  w..r..  saturat...!  with  n.oistnr..  at  a  t..<np..ra- 
tur..  of  1.-.     (".     A  hi-h  r.-lativ..  Innni.lity  at  a  hitrh  t.-nMn'mlur.. 
,„ak..s  ,t   inipossihl..  for  nan-h  swvat   t..  Im-  ..vai.orat...!.  with  tl... 
n.snlt  that  th..  l.o.iv  .-annot  .-..ol  prop.'rly.  an.l  tl...  ho.ly  1...ni...ra- 
tnr..  is  liUv  to  ris,.  unh'ss  nuisrular  a.-tivity   h,.   r...ln.-...l   to  a 
,„i„i„nnn.    This  ..xplai..s  why  it  is  in.p..ssibl..  to  .h.  nm.h  n,ns.u- 
L,r  work  in  hot  iu.n.i.l  atn.osph.r.s.     On  th..  ..th,.r  han.i.  .t  th. 

n.lativc  hun.i.Uty  is  h.w.  tin-  t...np..ratur..  .nay  ns..  f..  an  .-xtraor- 
.li,„,v  d..^nv..  (..v.-n  ahov..  that  of  th,.  l.o.ly  its..lf ,  wthont  .-aus- 
i„jj  iVv.-r.  provi.hHl  always  that  th.'  l.o.ly  is  not  s,,  .-..v.-.v.!  with 
cl.'thin!!  tliat  .-vaporation  of  sw.'at  is  in.|.ossihh.. 

\t  1..W  t,.M.p..ratur..s  of  tl...  air.  n.lativ.-  hnr.n.l.ty  has  an  ..tl.'.-t 
which  is  ..xa.-tlv  opposit..  to  that  whi.-h  it   has  at  h.jrh  t..nMM.ra. 
tmvs    for  now  it  aflV-.ts.  not  th..  ..vai.o..ati..n  of  sw..al.  bnt  th.- 

l,,,t    ...Muiu.-tivity   of   th,.   air    its..lf.      CoM    n.oist    a.r   .■on.ln.-ts 
nwav  h..M-n.u.-h  .u..r..  rapidly  than  ...hi  ,lry  ai.-.     Il.-n.-.    a  tyn.- 
p,.,.atur,.  u.a.iv  .U'^'n...s  l...|..w  yrvu  ....  th,.  .l.-y  j.la.ns  ol  tl...  W -.si 

,n,y  1...  M.n..l.   n.or..  tol..ral.h.  to  ...an  Iha..  a   ...uch   h.^'h..r  t...... 

p,.ratui...  alon^'  tl...  shor..s  of  thf  (iivat  Lak.-s 

Fever -\nv    ris.-   <.f   t(.n.p.'i-atur.>   al...v..    th,.    nor.nal    limits 
,-onstitut..s  f..v.r.     ^\\u^u  ..f  sli^'ht  <l,.-r...".  as  it   ,s  in  many  s....... 

acnt.'  .ns..as..s.    its  .l..t....li..n   .l.....a.,.ls    f..,,..,  ..t    ohs..rvat.oM,  so 

as  t..  alh.w  fo,.  tl...  ii..r..:al  .li..r..al  variati....  of  tli.-  l.o.ly  t..mp..ra- 

tur..      For  ..xampU..   if  tl...   t,.mp..ratur..   wr..   i..c..r.l...l   ui   th.. 


i:is 


I-IIYslOI.<NiY    KOK   UKSTAI-   KriDKNTS. 


mm  , 

i 


morning  in  sudi  ;.  pati.Mit.  a  slijtlit  (l.'«ivo  of  frvcr  inijflit  quit-' 
easily  !»<■  iiiiss.Ml.  iMcaiis.-  at  tliis  tiiii.-  tin-  noniial  t.'iiiiHTatmv  is 
low.  Ill  acut.-  inf.'ctioiis  <lis.-as.-s,  tli.'  aft.Ti.ooii  t.-m|..'ialmv 
niav  ris.'  to  KKi  K.  or  41  C,  or  .-wn  ahov.-  this,  with.nit  prov- 
ing' fatal.  A  trin|..rati.iv  of  ll:i  K.  or  4:.  C  has  Im.t.  ol.s(-rvr.l. 
l.iit  lastiiij;  for  only  a  short  time.  \u\<v  is  always  hi>rh.'r  in  in- 
fants and  youiijr  chihlrfu  than  in  aihilts. 

As  to  th'  Kins,  s  of  f(  VI  r,  two  possihiliti.-s  .'.\ist :  citli.T  ( 1  )  that 
h.-at  ].ro<luction  has  Imvm   iiirivasod.  or   Ci)   that  h.'at   loss  has 
Ihtu  (liiiiinish.Ml,  or.  of  cours.',  lioth  factors  may  oiM-rat.-  simiil- 
taiicouslv.    To  ^'o  into  this  unsolvc.l  prohl.-in  is  unn.'.-.'ssary  liciv  : 
sufti.-.-  it  to  say  that  tli.-iv  can  he  no  .loul.t  that  disturbance  in 
the  therinosfeiiic  centre   is  the   niKh-rlyiiiK  cause  of  fever,  and 
that  it   is  the  avenues  of  heat  loss  l.y  the  skin  ratlier  than  the 
sources  of  heat  sui-ply  in  the  muscles  tliat  are  first  of  all  acted 
on.     The  cold  sensation  down  the  hack,  the  shiv.-rin«.  the  jjoos,- 
.skin.  are  the  familiar  initial  symptoms  of  fever,  an.l  when  tiie 
fever  comes  to  an  end.  excessive  sweating'  sets  in  and  this,  in  i)art 
at  h'ast.  explains  the  fall  in  temperature     Increased  comlmstion 
in  the  musch-s  no  doul.t  occurs  during  the  heijjht  of  the  fever 
and  accounts  for  th.'  jireat  wasting',  hut  that  this  is  not  tho  only 
cause  of  the  rise  in  t.-mperature  is  ..videiiced  l.y  the  fact  that 
severe   muscular   exercise   does    not    in    itself   cans.-    fever,   even 
although  theiv  may  he  much  more  comlmstion  j>:oin<,'  '>n  m  the 
bodv  (see  J).  SSi. 

(•ertain  drugs  called  antipyretics  lower  the  temperature  in 
fever  Tlio  most  important  of  these  arc  aeetanilidc.  salicylates 
(aspirin).  phena<-etin.  and  .|uinine.  The  first  three  menti.med 
act  on  the  thermofrcnic  centre,  whereas  .piinine  seems  to  act 
directlv  on  the  combustion  processes  in  the  muscles.  The  body 
temperature  is  raisi-.l  by  cocaine  and  by  the  toxic  pro.lucts  of 

bacterial  growth.     Hveii  cultures  which  have  1 n  att.-miated  by 

keeping  them  for  s-ime  time  at  high  temi.eratuivs  have  this 
eff.'ct.  and  it  is  believe.l  by  nmny  that  fev.'r  is  of  the  nature  (.f 
ii  j>rotective  mechanism  to  destroy  or  attenuate  the  invadiii',' 
bacteria.  There  is  bacteriological  as  well  as  <linieal  sujiport  for 
this  view.  thus,  certain  patliogenic  r.-ganisms  '  such  as  the  strep- 


AMMAI'    IIK.AT    .\NI>    KKVKK. 


139 


t,K..u...us  Of  ..rvsip.-las^  oaM.u.t  livo  at  a  iHnp.-.at.uv  ahoo  41 
!;:,  Hw,l..nM>..tiH.ts  an.  nm..lMnon.  liU.ly  to  survm.  .t  th,.  .l.s. 

..„se  iH.  a.-.-on.|.anu-.l  by  a  n.o.l.rat.  .l.-«n-.'  of  f.-vr. 

p..^:;^:.  is  abovoth.  limits  of  saf..t>.     Wh..n  sw..at>n«  a,..l 
otla.r  ,.nu...sH..s  l,v  wl.iH,  l...at  is  lost  fr..n.  ,l-  boMy  a.v  aH- 
'    nro,u-  Iv  it  is  .v.narkabl..  bow  bi«b  an  a.r  t..n.,.-a1u.v  u,a> 
ri,n'wm..ntMan...r:for..xanM.b..in.lry,n^ 
L  son.,  n.inut.s  in  an  ov..n  at   100  (^  wb.b.  lus  ann.r  ...^^^^ 
,,..si.l..  bin.   (l.'onanl   llillK     H'.t   if  anyth,n«  shonM  .ntnt..  . 

will,  boat  loss,  or  if  b.-at  ,.n..luHion  1 x.-.-ss.v.-   as  .lnnn«  "U.s- 

,.„,,,.  .xen-iso.  tb.Mv  is  Mhvays  dan...-  of  boat  strok.-.  b  n-  n.ov.- 
,„,„t  „f  ,1,,  air  is  probably  tb.  n.ost  in„.ortant  way  t..r  sat.- 
.uanlin,  against  .l..H.-i.-..t  b..at  b.ss.  I,  is  almost  n-lam  y  on 
a.-.-onnt  of  tin.  abson.-..  of  sn-b  air  n.ov..>n..nt.  .-oupb..!  ^^.tl  a 
l.inh  .vlativ..  bun,i,iity.  tlu.t  .lis.-on.foH  is  ..xp-.n.-nn.  .n  bot. 
stuffv  atn>osplu.n.s.  for  lb.,  fa.illy  b.at  b.ss  .-ans-s  a  sl.jibt  nsr 
i„  hiuly  t..n.,H.ratun..  Tbis  sli«bt  .b'^-n-..  of  byporpyraxn,  low- 
ers iht'  n.sistanc.'  of  tb.-  ortranisni  to  inf..ction. 


CIIAI'TKIJ  XV. 
TIIK  liLOOl), 

Introduction.— The  iiulividiml  .'.lis  formiiiu  tlif  most  sin.j.l.' 
tvpcs  of   liff   arc    iiounshcd   l».v   suliHtaiics   wliidi    tlu'.v   ol.liiiii 
(li(vctly  from  tlif  wat.r  in  which  the  aiiiniiil  lives.     In  cxchaiiRc 
f()r  this  food,  they  cxcr.tc  into  the  water  tiie  waste  uiateriais  of 
their   iiietaholisni.      As   the   orKanisni    l.eeoiiies   more   and    more 
complex  this  direct  interciiantfc  of  materials  hcfomes  impossil)h'. 
un<l  the  l)l(K)d  and  lymph  assume  the  task  of  delivering  trnwl  to 
the  tissues  and  of  removinn  the  waste  materials.     To  accomplish 
this,  these  f1ui<iscome  intocliwe  relation  with  the  absorhin«,.lind- 
natiiiff.  and  pMiend  tissue  elements  of  the  ho.ly,  the  lymi)h  l.einy 
in  immediate  . ontad  with  the  cells  and  the  blood  moving  >{uU-k\y 
from  pla<'e  to  jdaee.     Th(  refori'  alJ  th.'  elements  fouml  in   tin- 
tissues  and  all  the  waste  materials  produced  by    the    body    are 
presei.t  at  some  time  or  another  in  the  bl(M)d.    The  bhxMl  may  in- 
deed be  eom|>ared  to  the  wholcsal.'r  of  commerce,  who  handles 
all  the  materials  for  the  support  of  life,  and  the  lymph  to  the 
retailer,  who  distributes  to  the  tissue  cells  the  nmterials  which 
th.-y  need.     In  short,  it  may  be  said  that  the  bUnxl  replenishes 
the  lymph  for  the  loss«-s  which  it  incurs  in  supplying  the  ti.ssues. 
Physical    Properties.— Ordinary    mammalian    blood    is    an 
opa.|\ie.  somev.hat  viscid  fluid,  varying  in  color  from  a  bright 
red  in  arterial  blood  to  a  dark  re.l  in  venous  Idootl.    Contact  with 
air  changes  venous  IiIcmxI  to  arterial  bliMxl.     Microscopical  exami- 
nation shows  thai   the  bloo.l  is  not   perfectly  homogenous,   but 
consists  of  a  clear  fluid  in  wliicli  cells  called  cori.uscles  are  sus- 
li'-'uled. 

The  Corpuscles. 

Tiin-..  are  three  varieti.-s  of  thes.-:  the  ml  lorjHisrhs  (to  which 
the  c.ioi'of  blood  is  duel,  the  irhilr  corinisch.t  and  the  hlooil 
pliilihts. 

140 


•^mi^^ 


^sfs=^^^m^ 


Tin:  Hi.fHin  cnui'ixi.K.s 


141 


Erythrocytes.  Th.  n,l  ,o,;»>s,l's,  ..>•  , n,ihn„„i.s.  as  tL-y 
an.  ...11..I,  H.V  by  far  th.  most  nuMH.nn.s.  th...y  l..-.n«  hv-  nnl^ 
li.,M  of  th...u  in  a  rul....  Mulli.-Ht.v  of  ....r.nal  I.I.hhI.  Kxanm....l 
>,„.l.,,.  ,h..  .ni.Tas...,,..-.  th..y  a.v  s.-n  t..  1m-  tlatt.M....l.  1,,-o.M-av.-. 

„ou.Mm-l..at.Ml  disrs  i.  .nan:  l.ut   in  tl n.hryo,  as  w-ll   as  .n 

hinis  an.l  .vptiLs.  tiny  hav  a  nu-l.-ns.  Kach  .•..r,.ns..i.  ..ons.sts 
„f  an  rnv.l..|M-  an.l  a  trannw<.rk  oC  |.rot.-in  an.l  l.p..Hl  n.at-nai 
contaiiiinj?  a  snl.stanc'  known  as  liH'ino«lol>in. 

U  KMo..i,oH.N  is  a  v.-ry  .-on.pl.-x  ho<ly.  h-lonfrinK  to  tii.-  «.n.ral 
..lass  of  .•..n.in,^.t..a  I>rofins  .s.-  p.  21  >•     lla-n.o«lol.M.  has  th- 
„l,ilitv   to   .-;•.    with  larjfr  amounts  of  oxy>f.-n.   thus  ..nahlin-i 
th.'  bi(K)a    "  .-.  n  •  the  oxy,r.-n  «ath.Mv.i  in  th.'  Innjrs.  to  th.-  .i.s- 
t.,„t  tissu.s      It  consists  of  a  ronihination  of  a  snnph'  prot.-.n. 
^lol,in.  an.l  a  i-iKMunt.  ha-n.atin.     Il<n„ati>,  n,„h,n,smuK  svhu-h 
is  tvsponsibU-  f..r  th.-  ability  of  oxy^.!.  to  unit.-  with  th.-  ha-n.o- 
irl„bin  ,Mol.-.-ul...     Th.-  .-on.bination  <.f  ha-n.onlob.n  with  oxy^.-n 
is  not  v.-rv  stabl.-.  a.ul  .-an  b.-  r.-a.lily  brok.n  with  th.-  l.b.-ration 
of  oxvu.-n"     It  is  for  this  n-ason  that  this  n...l.-.-ul..  is  a.lai.t.-.!  to 
..nn-v  ..xvp-n  to  th.-  tissu.s.     Th.-  .p.antity  ..f  ha-n...Klob.n  h.-l.l 
),v  tlH-  .-orpusH.-  may   vary  an.l  in  son..-  .lis.-as.-s,  as  n.  .-hl...-..- 
ana-mia.  f..r  instan.-.-.  it  niay  b.-  «n-atly  .liminish.-.l.  so  ...u.-h  s.. 
that  tin-  tissu.'s  nmy  b.-  unabl.-  to  ..btain  th.-  prop.-r  am.mnt  ot 
oxvK'."n     The  amount  of  ha-mo^clobin  a.-tually  pr.-s.-nt  in  a  samph- 
of'bloo.1  may  b,-  .-stimat.-.l  by  th.-  int.-nsity  of  th.-  ml  cm>  or  it 
eivfs  t<.  tin-  hhMMl     To  ,-stimat.-  this  int.-nsity  a  .Irop  of  bloo. 
is  m-.-iv.-.l  on  bl..1tins  pap.-r.  th.-  stain   b.-inK  th.-n  compar.-.i 
,.ith.-r  with  that  p.-.Hlu(-.-cl  by  normal  blo.).l  in  vari.uis  .lilutions 
„„  th.-  sam.-  pap.r,  or  with  a  stan.lar.liz...!  .-hart.    From  tlu-  con- 
,.,.ntrati..n  of  normal  bloo.l  whos.-  stain  most  noarly  match.-s  that 
of  th.-  unkn.>wii   sampl.'.  w.-  can   ,l.-tcrmin.-  tlu-   p.-rccntag.-  ol 
ha-mo-lobin  in  th.-  latter,  .>r  wc  can  rca.l  this  .lin-ctly  from  tli.- 

'  '*Enimek\ti..n  ..f  TiiK  BI..X.I)  CoRi-t  s(i,Ks.— The  numb.r  .)f  rc.l 
or  white  cells  pr.-s.-nt  in  a  cubic  millimetre  of  blood  may  b.-  esti- 
n.ateil  bv  th.-  us.-  ..f  a  ba-macytoinet.-r  or  blood-.-oimt.r.  This 
consists  i.f  two  mixiiiK  capillary  tubes,  in  one  of  which  th.-  blo.>.l 
,s  .lilui.-.l  ..ne  huh  =rcd  iin.es  with  salin^-  solution,  and  m  th.- 


m^^mm. 


142 


I'llYSIorifKlY    FOR   DKXTAIj   .STUDENTS. 


Other,  tiMi  times  with  0.'.V.i~'/,  Heetie  aeid.  Tlie  former  dilution  is 
for  counting  red,  and  tlie  latter,  for  eountinsr  white  eorpuse]e.s. 
A  drop  of  the  diluted  blood  is  then  i»laeed  on  a  speeial  glass 
slide  whieh  eontains  a  (•ountiii'':  ehamber  of  sueli  a  de|)th  that 
when  a  eover  .slij)  is  ])ut  over  a  drop  of  Huid  in  the  ehamber,  a 
polumn  of  fluid  one-tenth  of  a  millimetre  deep  is  obtaineil  (Fig. 
13).  The  chamber  is  graduated  with  cross  lines,  so  that  each 
s<|uare  rej)resents  a  known  fraction  of  a  millimetre.  The  average 
number  of  corpuscles  found  in  a  nu'nber  of  s(|uares.  by  actual 
count  with  a  microscope,  is  multiplied  by  the  factors  of  dilution 
employed,  the  product  being  the  number  of  cells  in  a  cubic  niilli- 


0.100mm. 


C.  Zeiss 
Jena. 


KiK.  13.— Thoma-Zoi.ss  Haemocytoni.'ter ;  .\r.  mnutlipieoi'  of  tube  (O).  by 
wliich  lilood  iM  Kuiki'd  into  .v.-  H.  bead  for  mixiriK;  n.  view  of  slide  frimi 
ulM)ve  ;  h.  in  section;  r.  xijuares  in  niiddl<>  of  H.  as  sieii  under  niieroscoiie. 

nu'tre  of  blootl.  The  erythrocytes,  whieh  in  health  number  about 
five  million  in  a  cubic  millimetre,  may  decrease  to  less  than  a 
million  in  disease,  such  as  ixrnicious  anaMuia.  or  after  hasnior- 
rhage.  On  the  other  hand,  they  may  nund)er  six  or  seven  million 
in  people  who  live  at  high  altituch's.  The  oxygen-carrying  power 
of  the  blood  is  ijrojjortional  to  the  jjercentage  of  haemoglobin,  so 
that  by  estimating  this  and  the  number  of  corpuscles,  a  fair  idea 
of  the  eonditi(m  of  the  blood  is  obtained. 

The  Origin  of  Krvtiikocvtes. — It  is  interesting  to  incpiire 
into  the  source  of  the  blood  cells,  but  although  this  has  been  the 
subject  of  many  researches,  it  is  by  no  means  definitely  settled 


ani 


Till-;  lu.ooi)  rui{i'rs('ij;s. 


143 


just  vvliat  tlic  i)nx'i'is.s  is  or  in  wliat  i)art()f  tliobody  the  eolls  orifji- 
iiatc.  Nor  is  it  definitely  known  just  wiiere  tlie  worn  out  eells 
are  dealt  with.  Jn  the  embryo  certain  cells  are  set  ai)art  to 
develop  the  vascular  systei;;.  Some  of  these  form  the  blood  ves- 
sels and  some  the  red  eor])uscles.  but  later  in  fo'tal  life,  the  latter 
come  from  eells  in  the  spleen,  liver  and  red  bone-marrow.  At 
first  the  red  cori)Uscies  are  nucleated,  but  towards  the  end  of 
fo'tal  life  they  begin  to  lose  their  luiclei.  so  that  at  birth  there 
are  very  few  nucleated  red  corpuscles  reinainiiifi  in  the  blood. 
After  birth,  the  red  corpuscles  are  formed  in  the  retl  bone-mar- 
row of  the  flat  bones.  In  these  i)laees  s])e('ial  luicleated  eells  arc 
found,  which  are  called  erythroblasts,  and  from  these  the  ery- 
throcytes develop.  After  severe  hiemorrhage  nucleated  red  cells 
may  api)ear  in  the  bl(R«i  for  a  siu)rt  time;  the  same  is  true  in 
some  forms  of  ana'mia  in  which  there  occurs  a  very  rapid  destruc- 
tion accompaiued  with  a  very  rapid  formation  of  red  cells. 

Since  the  life  of  a  i  rj/llirvcijlr  is  necessarily  limitetl,  provision 
must  be  made  for  the  <lestruction  and  elimination  of  the  sub- 
stances of  which  they  are  composed.  In  the  i»ifrmeiits  of  the  bile 
we  find  the  remains  of  j)art  of  the  ha-moglobin.  The  bile  is 
secreted  by  the  liver  into  the  intestine  (see  j).  71).  and  in  case 
the  free  outflow  of  bile  is  intei'fered  with,  the  blood  absorbs  the 
pijrment  and  the  individual  Ih'cop.cs  yellow  or  is  said  to  be  jaun- 
diced. The  bile  pigTiients  do  not,  however,  contain  all  the  ele- 
ments of  the  liaMiioglobin.  for  the  iron  is  not  e.xcreted  l>y  the  bile. 
It  is.  on  the  contrary,  stored  U])  by  the  liver  to  be  used  again 
in  tile  formation  of  fresh  ha-moglobin.  Some  have  thought  that 
the  function  of  the  spleen  is  to  destroy  the  nd  blood  alls,  the 
waste  i)roilucts  of  which  are  sent  to  the  liver  through  the  .splenic 
vein.  The  evidence  for  this  is  the  [)resence  of  pigment  and  iron- 
containing  substances  in  the  blootl  of  this  vein. 

Iron  is  an  essential  constituent  in  the  ha'moglobin  molecule, 
and  it  is  n(>ee.ssjiry  that  sonu>  be  constantly  supi)lied  to  the  body 
in  the  food.  But  this  amount  need  not  be  large,  since  the  iron- 
containing  substance  can  be  used  time  and  again  in  the  manu- 
facture of  new  ha'moglobin,  and  once  the  body  has  the  re(piisite 
amount,  little  more  need  be  added   (see  p.  120).     Indeed,  it  is 


144 


l'IIVSI(lI,()(iV    KOK    DKNTAI,    STIIIKNTS. 


quostioiiabit'  if  tlic  iiiortraiiic  forms  of  iron  can  be  utilized  by  the 
body,  tlif  iron  in  our  bl(MHl  bciiii;  probably  derived  from  a  con- 
jugated protein  known  as  lucmatofreii.  found  in  small  (|iiantities 
in  the  food. 

The  White  Blood  Cells.— In  normal  liunian  blood  tlien-  are 
about  ten  thousand  cells  in  a  cubic  millimetre  of  blood,  or  about 
one  to  every  five  hundred  val  cells.  In  many  ways  they  resemble 
the  luiicellular  amu'ba.  for  like  it  they  have  the  power  of  makinjr 
indei)endcnt  movement  by  extendinj;  tiny  |)rocesses  called  pseu- 
dopodia  in  one  direction  and  by  retracting'  them  in  another.  In 
virtue  of  this  peculiai'  movement  they  are  able  to  flow,  as  it 
were,  between  the  en<lothelial  cells  of  the  capillaries  and  tind 
their  way  into  the  tissue  spaces.  There  are  a  number  of  forms 
of  white  cells  differinjr  from  each  other  in  size,  in  character  of 
their  nucleus,  and  in  tln'  jL'ramiles  they  contain.  In  ireneral.  they 
are  cla.ssitie<l  in  two  main  {.'roups  on  inor])holo}:i"  ,'rounds,  viz.. 
hi((Ot  lifts  and  liim})hiii  fill  s. 

Thi   Lt  ucoculi .-<  are  tlie  most  iiumero\is  an  lose  about  ti.') 

]>er  cent  of  the  total  whiti lis.     They  are  -terized  by  a 

lobed  n\icleus.  the  parts  of  which  are  connected  by  strands  of 
chroniatin  nuiterial.  To  this  class  belong  several  sub-<iroui)s. 
The  most  iin|)ortant  of  these  are  the  cells  known  as  i)olymorpho- 
iMiclear  leucocytes.  They  coni|>rise  about  !>(>  per  cent  of  the 
leucocytes.  Another  type  are  known  as  eosinophyles.  since  they 
have  granules  with  a  marked  afTtinity  for  acid  stains. 

Thr  L\imph(n!iU s. — The  second  variety  are  so-called,  since 
they  are  sui)posed  to  be  formed  in  the  lym]ih  <j;lands  of  the  body. 
They  possess  a  -lUfrle  lartre  round  r.ucleus  surrounded  by  a  clear 
layer  of  ])rotoi)lasni.  There  are  two  snb-^'roups  in  this  class; 
the/iav/f  iiioiiiiiiiK h iir  }timi>h<)(  ijlis,  which  contain  a  rather  abun- 
dant cytoi)lasin  about  the  nucleus,  and  the  snuill  monoiniilinr 
himphonjifs,  in  which  the  anumnt  of  cytoi)lasm  is  very  small. 
The  former  comprise  about  4  |»er  cent,  and  the  latter  about  :{() 
per  cent,  of  the  white  ci'lls. 

EsTlM.\Ti(tN  OK  TiiK  WiiiTK  ( 'km.s. — Tile  number  of  white  cells 
found  in  the  l)lood  is  estimated  by  the  sanu'  jtriiu-iple  that  is  em- 
ployed in  the  counting  of  the  red  cells  (see  p.  142).     In  certain 


k 


mm 


THE    BLOOD    PLASMA. 


14.-, 


diseases  tlieir  iiuiiiImt  iiwiy  vary  greatly.  Tli(>  nunibi'r  is  also  in- 
creased after  meals.  A  marked  inerease  over  normal  is  known 
as  a  loueccytosis. 

The  FiNCTioN  of  the  LEtTocVTES. — In  aeute  iiifeetions.  as 
in  appendicitis,  pneumonia,  and  Iwalized  or  jjeneral  sej)tie  con- 
ditions in  wliicli  jms  is  formed,  there  is  usually  a  great  inerea.se 
ill  the  number  of  the  polymori)lionuclear  leucocytes.  In  more 
clironic  infections,  as  in  tuberculosis,  the  lymphocytes  are  found 
ill  greater  numb  -r.  In  the  parasitic  diseases  of  animal  origin,  as 
tapeworm  and  hookworm,  in  some  skin  diseases,  and  in  scarlet 
fever,  tlie  e()sino})hile  leucocytes  are  more  abundant.  In  the 
disease  leuccK'ytha'inia  tlie  lymphocytes  may  be  present  in  such 
great  numbers  that  they  impede  the  movement  of  blood  by  iu- 
creasiig  its  viscosit.\  or  thickness.  The  above  observations  sug- 
gest that  leucocytes  ])lay  an  important  role  in  the  protection  of 
the  body  from  infective  processes.  This  function  will  be  dis- 
cussed later.  Another  important  function  they  may  have  is  the 
preparation  of  the  peculiar  i)roteiiis  which  are  found  in  the 
blood  i)lasma. 

Tih:  ]?L(«)d  Platpxet.-^.— -These  bodies  are  smaller  than  the 
erythrocytes,  and  nund)er  about  :}00.000  in  a  cubic  millimetre 
"f  bl(K)d  When  blood  is  slied  they  disintegrate  very  rapidly, 
and  s«'t  free  a  sub.stance  which  plays  a  part  in  the  coagulation  of 
the  blood.  Little  is  known  concerning  their  dieiiiical  constitution 
or  their  physiological  function. 

The  Blood  Plasma. 

The  blood  jilasma  is  a  very  complex  Huid  containing  all  the  va- 
ried substances  associated  with  tlie  function  of  the  blood.  Water 
composes  f)0  per  cent  of  the  plasma.  The  plasiii;i  proteins  consti- 
tute the  largest  solid  constituent  (7  per  cent),  and  inclmle  ^^.nnn 
idnlilllin.  smu"  all^"'")"'  and  fibrinogeii.  There  are  a  number  of 
bodies  which  contain  nitrdgen  which  are  not  proteins.  These 
mny  be  grouped  into  two  cla.s.ses.  the  first,  represented  by  the 
amino  acids  and  other  nitrogenous  bodies  derived  from  the  pro- 
tein of  the  food  and  from  which  the  tissue  cells  are  built,  and  tiie 
second  group,  represented  by  waste  materials  given  off  by  the 


146 


IMiySIOLCKiY    KOR    OENTAI.    STIDENTS. 


tissue  colls.  Tht'so  includt'  substaiipt-s  sncli  as  iiroa.  uric  acid, 
crcatiiiiu,  ami  ainiiionia.  The  iioii-nitrnp-uoiis  orfjaiiic  bodif^-  arc 
dextrose,  of  which  0.1  percent  is  present  in  normal  i)lasina.  and  a 
small  t|uaiitity  of  fat.  About  1  l>er  cent  or  inorganic  salts  are 
found,  the  chi«'f  of  which  is  sodium  chloride,  which  constitutes 
fiO  per  cent  of  tiie  ash.  So<lium  carbonate  is  found  in  a  little  less 
degree.  Besides  these  two  we  find  small  amounts  of  potassium, 
sodium  and  calcium  chlorides  and  plio.sphates.  An  important 
grouu  of  substances  known  as  hormones  are  excreted  into  the 
p'  \.sua  by  some  of  the  glands  of  the  body,  and  aftVct  the  meta- 
bolism of  the  tissues  in  a  s[)ecific  manner.  Another  group  of 
bodies,  the  antitoxins,  comidements.  and  opsonins  (see  \).  124), 
are  fouml  in  the  blood.  These  are  concerned  in  the  protection  of 
the  body  against  infective  organisms. 


CIIAPTEH  XVI. 
THE  BLOOD  (CoiitM). 


The  Defensive  Mechanisms  of  the  Blood. 

The  Coagulation  of  the  Blood.— Whenever  a  blood  vessel  is 
slightly  cut,  the  bloml.  which  at  first  eonies  very  freely,  soon 
eeases  to  flow  beeause  of  the  formation  of  a  plug  or  elot  of  blood 
at  the  site  of  the  injury.  The  process  by  which  the  blood  spon- 
taneously forms  the  plug  in  the  injured  vessel  is  known  as  coagu- 
lation, or  clot  formation.  It  protects  the  bo«ly  from  fatal  hem- 
oi-rhage  in  case  of  an  ordinary  wound.  A  clot  is  a  semi-solid 
jiiass,  which  on  microscopical  examination  is  seen  to  consist  of  a 
me.shwork  of  fibrils  holding  the  blood  corpuscles  in  their  inter- 
spaces. If  blood  is  collected  in  a  basin  and  whipped  with  some 
twigs  while  it  is  clotting.  *he  fibrils  will  collect  on  the  twigs  in 
stringy  masses,  and  the  'lood  will  remain  fluid.  The  stringy 
material  is  called  fibrin.  Obviously,  fibrin  cannot  exist  in  the 
blood  stream,  else  the  blood  would  form  a  clot  within  the  blood 
vessels ;  it  is  formed  only  when  occasion  demands,  such  as  an  in- 
jury to  the  blood  vessel.  There  are  a  nundx-r  of  experiments 
which  explain  the  process  of  coagulation. 

Thus,  if  blood  is  prevented  from  clotting  by  cooling  it  to  0." 
centigrade,  and  is  then  mixed  with  a  saturated  solution  of  salt, 
a  white  precipitate  forms,  which  may  be  filtered  off  and  dissolved 
in  0.1  per  cent  salt  water.  This  solution  may  be  made  to  clot  by 
the  addition  of  a  very  little  blood  from  which  ihe  fibrni  has  been 
removed.  In  other  words,  we  have  prepared  a  substance  which 
under  proper  conditions  forms  the  fibrin  of  the  clot.  This  sid)- 
stance  is  called  fibrinogen,  since  it  is  the  jireeurser  of  fibrin. 

Again,  if  blood  be  treated  with  sodium  oxalate,  it  will  not  clot 
unless  caliium  s<ilts  be  added  in  amount  sufficient  to  precipitate 

147 


148 


PnySIOI.OGY   FOR   nENTAIi   STt'DKNTS. 


eoiiipli'tfly  all  the  oxalate  and  leave  some  in  exe«'ss.  In  other 
words,  tlie  i)resence  of  a  soluble  ealeiuni  salt  is  neeessary  in  order 
to  have  the  blootl  elot.  Defibrinated  blowl  will,  however,  eause 
the  clotting  of  pure  fibrinogen  solutions  even  though  all  the  eal- 
eium  be  removed  from  both  solutions. 

In  order  to  explain  the  above  facts,  we  must  assume  that  three 
substances  are  present  in  solution  in  the  bloo<L:^jiiri/ii2fli:'i,^<  "'- 
ciiim  salts,  and  another  substance,  which  has  been  called  throm- 
_bogrn.  Under  the  proper  conditions,  thrombogen  will  combine 
with  calcium  salts  to  form  thrombin,  which  in  turn  unites  with 
fibrinogen  to  form  fibrin,  which  is  the  substance  forming  the 
framework  of  the  clot. 

The  reason  why  the  blood  does  not  clot  within  the  blood  ves- 
sels is  not  definitely  known.  It  is  probable  that  the  blood  con- 
tains a  substance  which  prevents  the  combination  of  thi-ombogen 
with  calcium  salts,  and  which  we  call  anti-thrombin.  Wlicnever 
a  blood  vessel  is  injured,  tlie  tis.sues  and  the  blood  platelets  liber- 
ate a  lii)oid  body  called  krpltnhv,  which  unites  with  the  aiiti 
thrombin  and  thus  allows  the  formation  of  thrombin  to  take  place 
at  the  sit(  of  the  wound.  Tlie  whole  process  may  be  graphically 
shown  in  the  following  schema : 

Anti-thrombin  +  kephalin  =  inactive  anti-thrombin. 
Thro    'jogen  +  calcium  salts  =  thrombin. 
Thrombin  +  fibrinogen  =  fibrin. 
Fibrin  +  corpuscles  =  clot. 

Antibodies  in  the  Blood.— Tlie  coagulation  of  the  blood  is 
only  one  of  the  measures  which  are  developed  in  the  blood  for  the 
protection  of  the  animal.  No  less  important  in  this  regard  are 
the  destruction  and  removal  of  toxic  and  injurious  substances 
from  the  botly. 

All  the  infectious  diseases  are  caused  by  the  agency  of  micro- 
organisms. The  greater  number  of  these  are  microscopic  plants 
known  as  bacteria  and  fungi ;  some,  however,  are  unicellular  ani- 
mals known  as  protozoa.  It  is  especially  against  the  bacteria  that 
a  method  of  defense  exists  in  the  body ;  the  protozoal  diseases,  on 


THE   DEFENSIVE    MECHANISMS   OK   THE    Br,«HiI>. 


149 


tho  other  liaiul— such  as  nyphilis,  Tiialaria.  slocpiniu'  si«'kiifss  ami 
tliost'  caused  by  aimi'ba  in  the  mouth  aii«l  alimentary  traet— tind 
rehitively  little  resistance  offered  to  the  ingrowth  in  the  body,  and 
their  destruction  therefore  must  be  for  the  most  part  brought 
about  by  drugs. 

The  Process  of  Inflammation,  wincii  in  a  general  way  is 
known  by  tho  common  symptoms  of  fever,  pain,  swelling  and 
redness,  is  a  sign  of  an  increased  activity  on  tlic  part  of  tiie  tis- 
sues in  an  effort  to  destroy  sonie  foreign  body  which  is  poisonous 
to  tho  cells.  Microseoj)ical  cxannnation  of  a  st'ction  of  inflamed 
tissue  will  show  that  the  blood  vessels  arc  dilated,  and  tliat  the 
tissue  spaces  are  infiltrated  with  leucocytes.  It  suggests  that  the 
blood  elements  must  have  a  very  important  part  in  the  process. 
The  study  of  this  function  of  the  body  is  one  of  the  most  inter- 
esting cliapters  of  physiological  science,  and  includes  the  ques- 
tions of  immunity  from  disease  and  the  cure  of  infectious  pro- 
cesses. 

Many  pathogenic  organisms  can  be  cultivated  on  artificial 
media  and  the  products  of  their  metabolism  can  then  be  studied. 
It  has  been  found  that  they  nuiy  be  divided  into  two  groups;  the 
one  group  producing  the  soluble  poisons,  or  true  toxins,  which 
are  excreted  from  the  cell ;  and  the  other  group  producing  toxic 
substances,  tiie  endo-toxins,  which  are  not  excreted  from  the  cell. 
We  will  first  take  up  the  nummr  in  which  the  body  deals  with 
the  toxins. 

Toxins.— If  a  culture  of  diphtheria  or  tetanus  bacilli  be  fil- 
tered through  a  porcelain  filter,  the  bodies  of  the  bacilli  are  re- 
moved and  the  filtrate  contains  the  soluble  toxic  principles  which 
the  bacilli  have  produced  and  excreted  into  the  nutrient  fluid. 
Injections  of  a  small  amount  of  this  filtrate  into  an  animal  will 
l)roduce  the  same  symjitoms  as  are  produced  when  a  pure  culture 
of  the  bacilli  is  injected.  Kach  bacilhis  produces  a  specific  kind 
of  toxin.  Diphtheria  toxin  acts  i)rimarily  on  the  vasc\dar  sys- 
tem ;  tetanus  toxin,  on  the  central  nervous  system.  The  chemical 
luvture  of  the  toxin  molecule  is  unknown,  since  it  has  been  impos- 
sible to  sepai'ate  it  in  pure  form.  It  is  i)robably  closely  related 
to  the  protein  mok-c-ulo,  and  ou  the  other  hand  resembles  the 


150 


I'llYSIOMKiY   FOR   DENTAL   STIDENTS. 


t'cniu'iits  ill  many  of  its  aetioiis  (sw  p.  ;{4).  A  pfciiliaiity  in 
the  action  of  the  toxins  is  tiiat  a  relatively  long  period  elapses 
between  the  injection  of  tiie  toxin  and  the  reaction  of  the  body, 
whereas  in  the  ease  of  the  alkaloids  or  vegetable  poisons,  the  re- 
action appears  very  <|iiickly. 

Antitoxin.  —In  spite  of  the  very  poisonous  character  of  tlie 
toxin  molecule,  the  body  is  provided  with  a  means  of  defense 
against  it,  and  is  able  to  make  itself  still  further  immune  to  the 
action  of  the  toxin.  Thus,  if  somewhat  less  than  the  fatal  dose 
.)f  diphtheria  or  tetanus  toxin  be  in,jected  into  the  body,  certain 
symptoms  will  follow,  and  tlie  animal  will  react  to  the  toxin  in 
such  a  way  that  a  subsecjueiit  injection  can  be  made  larger  with- 
out proving  fatal.  If  successively  increasing  doses  are  given,  the 
animal  after  some  weeks  will  be  able  to  withstand  very  large 
doses  of  the  toxin.  In  other  words,  the  body  develops  an  im- 
nuinity  towards  the  toxic  agent;  it  i)roduces  an  antibody  which 
ne\itrali/es  the  poison  of  the  toxin.  To  this  body  we  give  the 
name  of  antitoxin.  Since  these  antibodies  are  found  in  solution 
in  the  l)loo<l,  it  is  i)os.sible  to  withdraw  the  blood  from  such  an 
immune  animal,  and  inject  it  into  a  non-immune  animal,  thus 
rendering  tlie  latter  immuiu'  to  the  toxin.  It  is  this  principle 
that  is  used  in  the  preparation  of  diphtheria  and  tetanus  anti- 
toxins. The  exact  nature  of  the  combination  of  the  toxin  and  the 
antitoxin  cannot  be  learned  from  chemical  .studies,  but  Ehrlich 
has  given  to  the  phenomenon  a  biological  explanation  based  on 
the  various  known  reactions  of  the  botUes. 

Ehrlich's  Side  Chain  Theory  of  Immunity. — Briefly  summar- 
i/A'd  Ehrlich's  theory  is  as  follows:  Each  toxin  molecule  is 
mailc  up  of  a  central  nucleus  of  chemical  radicles  similar  to  those 
found  in  organic  compounds.  To  the  main  body  of  this  mole- 
cule are  attached  at  least  two  other  radicles,  or  side  chains.  One 
of  these  has  a  great  affinity  for  certain  chemical  constituents  of 
the  tissues  of  .susceptible  animals,  and  unites  the  toxin  molecule 
to  the  tis.siie  cell.  This  chain  is  known  as  the  haptophorc  (ffoiip. 
The  other  side  chain,  the  ioxophon  </roiip,  exerts  the  injurious 
effect  upon  the  tissue  after  the  haptoiihore  group  has  joined  the 
toxin  to  the  cell.     For  example,  tetanus  toxin  owes  its  effect  to 


TlIK    OKFKNSIVK    MECHANISMS    OF    TIIK    BI.<M)n. 


ir.i 


till'  fact  Unit  iKTVOiis  tissiio  coiitirms  a  chcinical  substance  whicli 
unites  readily  with  the  hapt(>i)hitiv  ki-oui)  of  the  tetanus  toxin, 
and  also  suhstanees  that  are  readily  attacked  by  the  toxophore 
Uroiip  of  the  toxin.  The  antitoxins  are  supposed  to  act  by  com- 
bining with  the  haptophore  jrroui).  thus  preventiuK  the  toxin 
from  uniting  with  the  cell. 

Accordint,'  to  this  theory  the  formation  of  antitoxins  may  be 
accounted  for  as  follows;  When  a  rrcrpfor,  as  we  nniy  term  tlu- 
portion  of  the  <'ell  which  unites  with  ha|)tophore  ^'roup.  is  united 
to  the  toxin,  the  cell  endeavors  to  ada|)t  itself  to  the  loss  of  this 
radicle  by  the  prodiu-tion  of  another  similar  one.  Since  the  gen- 
eral rule  of  nature  is  to  resi)ond  to  an  action  with  an  over-reac- 
tion, many  more  receptors  are  made  than  are  actually  needed  to 
luiite  with  the  hai)toi)hore  Kroui>s  of  the  toxin  present.  The  re- 
ceptors produced  in  such  «reat  number  break  away  from  the 
liarent  cell.  These  accordinifly  are  stored  up  in  the  blood,  and 
whenever  any  of  the  partieular  toxin  for  which  they  are  adapted 
is  present  in  the  circulation,  they  unite  with  it  and  thus  prevent 
the  toxin  from  uniting  with  the  tissiie  cells.  A  body  which  pos- 
sesses   a    store    of    such    antibodies    i^    said    tlu'refore    to    be 

immune. 

Toxins  are  not  the  only  substances  which  will  produce  specific 
antibodies.  This  property  is  a  general  characteristic  of  proteins. 
Any  sub.stance  producing  an  antibody  is  known  as  an  antigen. 
For  example,  if  liunuin  blood  be  in.jt'cted  into  a  rabbit,  and  after 
several  days  some  of  the  rabbit's  blooil  serum  is  mixed  with  hu- 
niaii  blood  serum,  a  precipitate  will  form,  whereas  the  blood  of 
a  normal  rabbit  will  produce  no  such  precipitate.  The  first  in- 
jection of  hviman  blood  serves  to  stimulate  the  rabbit  cells  to 
form  some  substance  which  precipitates  any  human  blmnl  sub- 
sei|Hently  added.  The  reaction  is  specific,  for  the  blood  of  any 
other  species  of  animal  will  not  be  precipitated  by  blood  from  a 
rabbit  sensitized  with  human  blood,  and  the  reaction  otfers  a  very 
accurate  method  of  differentiating  Ix'twceii  hunuin  blood  and 
othei-  blood  in  medico-legal  cases.  The  body  t.ius  formed  is  known 
as  a  pnripilin. 

Anaphylaxis.— Again,  if  a  rabbit  be  injected  with  some  liu- 


152 


I'lIV  ilOLOUY   KOR   DENTAIj   STl'DENTS. 


iiiiui  .sciniiu  two  or  tliroc  wt'cks  aftci-  a  previous  iiijtM'tioii,  tin- 
aiiiinal  will  go  into  a  vt'i-y  profouii*!  stati-  of  sliork.  The  IiIo(m1 
pressure  will  be  lowered,  the  heart's  action  weal<ene(l.  and  breatii- 
injf  interfered  with.  This  eondition  is  i<Mown  as  anaphijUnlic 
shuck.  The  reaction  is  a  general  one  for  proteins  and  is  si)i'eifi(; 
for  eaeii  protein  used.  The  phenomenon  is  e.xplained  by  a.ssuni- 
ing  that  tiie  first  injection,  while  producing  the  IxMlies  wliieli  we 
referred  to  above  as  precipitins,  also  j)roduces  an  excess  of  u  fer- 
ment wliich  is  able  to  l)r(iik  down  the  foreign  jirotein  very  (piick- 
ly  when  the  s«'eond  injin-tion  takes  places.  '  tie  products  of  the 
broken  i)rotein  moh'cule.  as  they  are  prodiiccil  in  the  blood,  are 
poisonous  to  the  body  and  ■  -oduce  the  phenomenon  above  dc- 
scribe<l. 

PhagfOCjrtosif. — \\y  far  ic  greater  nund)er  of  patliogeuie  or- 
ganisms do  not  excrete  a  poisonous  toxin  into  the  surrounding 
medium,  but  they  cause  disease  by  directly  attiieking  the  tissues. 
The  diphtheria  bacillus  does  not  enter  the  body,  but  only  ex- 
cretes a  soluble  toxin  which  the  body  absorbs.  When  the  diseasi' 
involves  the  infection  of  the  ti.ssues  them.selves  by  a  micro-or- 
ganism, other  types  of  defense  than  those  described  above  are 
u.sed.  This  defense  ilepends  on  the  fact  that  S(»me  of  the  leu- 
cocytes of  tile  blood  and  lymph  have  the  ability  to  ingest  and  de- 
stroy foreign  bodies  which  are  present  in  the  blood  and  tissues, 
in  much  the  .same  way  that  the  amceba  takes  its  food.  This  func- 
tion of  the  leucocytes  to  destro.v  foreign  bodies  is  known  as  phn- 
yocytuftis.  In  the  changes  which  accompan.v  the  metamorphosis 
of  certain  forms  of  larva,  the  leuc(M'yt<'s  are  the  agents  which  re- 
move those  i)ai"ts  of  the  body  wbicii  are  no  longer  of  service  to 
the  animal.  Likewise  tlu'  leucocytes  of  the  blood  can  be  shown 
to  ingest  pathogenic  bacteria  and  to  destroy  them.  There  are  a 
number  of  varieties  of  white  cells  in  tlie  blood,  and  uj)  to  this  time 
the  part  played  by  each  is  not  definitely  known.  In  active  in- 
flammatorv  processes  the  [mlymoiplioiiudear  leucocytes  are  by 
far  the  most  numerous.  On  the  other  hand,  in  cases  of  chronic 
infection,  as  in  tuberculosis,  the  nnnd)er  of  lymphocytes  is  in- 
creas«'d.  Some  of  the  forms  of  white  cells  do  not  take  an  active 
l)art  in  the  ingestion  of  bacteria,  and  therefore  cannot  directly 


TIIK    KKKKNSIVK    MKCII AM^'MS    OK    TlIK    lll.(Hll» 


!,-.;{ 


(li'sti'oy  tlifiii.  Yet,  ill  the  tlffrriw  tit"  the  orixiiiiisni.  Ilicy 
tiikf  a  iiai't  which  m  iit>  Iish  iinixiitaiit  than  that  i>l'  thi- 
l>ha^()c\  tf. 

Ill  very  siiii|>h'  I'ortiis  of  life  the  cells  of  tlic  aliiiu-ntai'v  tiact 
hoth  iiip'st  iiti<|  digest  the  food  inatcriiil.  In  hi<;hi  r  fui-iiis  the 
cells  of  the  iilinicntary  tract  secrete  the  llniils  wliieh  difjest  the 
food.  In  the  one  case  tlie  digestion  is  intra-cellnlar.  and  in  the 
latter,  extra-ceiluliir.  In  tlic  same  way  we  find  the  hlood  leu- 
cocytes ahle  hoth  to  (hstro\'  and  to  dijfcst  snhstaiiees  liy  intra- 
(.•ellnlar  action,  and  also  sjiiirinj;  with  other  cells  of  the  hods  the 
power  to  secrete  siihstiinces  into  the  hlood  plasma  which  have  the 
power  of  destroyiiijr  the  ori^anisms  or  toxic  mati'rial. 

Opsonins. — Norma!  hlood  serum  has  a  very  strong,'  destrnc- 
ivc  infliience  on  most  sj)ccies  of  hactcria.  whether  they  arc  patho- 
ireiiic  or  not.  This  ahility  is  not  possessed  to  the  same  extent  li\' 
the  hlood  plasma.  The  ditrereiice  is  exjiliiined  l)y  the  fact  that 
ill  the  procc.ss  of  eoafjulation  the  white  hlood  cells  are  hroken 
down  and  lihcratc  tin'ir  hactericidal  bodies.  lOxtraets  in.ide  of 
leucocytes  have  this  saiiie  elVict.  but  the  n'aetion  is  much  more 
rapid  in  the  pri'sonce  of  bhxtd  jilasma  or  s.'riim.  The  co-oper- 
ation on  the  part  of  tlic  plasma  or  serum  is  explaiiud  by  the 
presence  of  sonic  substance  in  solution  which  eiialijcs  tlic  leu- 
cocytes the  more  readily  t<t  attack  the  bacteria. 

That  some  such  substances  also  aid  in  the  pliaijocytic  action  of 
the  leucocytes  is  indicated  by  the  fact  that  the  white  cells  injjest 
bacteria  much  more  readily  in  Mood  seriini  than  in  normal  saline 
solution.  These  substances  arc  known  as  opsonins,  and  are  char- 
acteristic for  each  individual  or<raiiism  which  stimulates  their 
l)roduction.  At  the  beginniii'r  of  an  infective  process,  in  which 
the  phaj^ocytosis  is  very  active,  eacn  leucocyte  iiia\'  be  al>le  to  at- 
tack only  one  or  two  bacteria  ;  later  in  tiie  disease,  however,  when 
the  opsonic  power  has  }>een  increased  for  the  infective  ajreiit.  the 
leucocytes  may  be  aiile  to  iiij.rest  a  much  I,ir;rcr  number  without 
in.jury  to  themselves.  The  opsonic  index  is  a  ti^iire  cx|)ri'ssin<r 
the  ratio  of  the  number  of  piitli(iy:eiiic  orffanisms  id'  a  ••ertaiii 
kind  that  a  normal  leucocyte  can  inj^cst  in  serum,  to  that  which 
the  same  leucocyte  can  iiiijest  in  the  presence  of  tiie  serum  of  a 


\.*4 


l'IIVXH>I.IKi\     KUK    uKNTAt.    ST^!>K^T^ 


piit'ciil   who  is  stifffriiiK  from  flu    mf.itivc  ajfi'iit       A  !iitfli  op 
H:i;.ic  iiul.  \  tlu-rt't'on'  indicati-s  h  rflativt-  iniiimnity  or  liifth  r  ^int 
ancf  1o  tht'  iliscasc  in  i|vitstion.     The  hjii-tfricidal  (towt-r  "i   the 
leu»'o«'yt«'H  for  many  hacti-ria  i-ari  he  >jri>atly  incrcawtl  In  th'    in- 
joctiuii  of  (Icii'l  h-.M'U  lia  iiilo  flic  hoily.     This  fart  In  ^.inli-  uw-  "f 
in  thi'  inHMiifa<'tur'    of  hai'tfrial   vaci'in«-s.  whirh  con^iHt  of      i> 
pensions  (»f  dt-ad  haciiria  in  salint 


ClIAITKi     X\  II 
TFIK  h^  MIMI 
Tlif  1iI(mmI  cinuliitcs  in  fli)>«u  tiiln 


wliicli  is  supplifd  111!'  tissues 
suit  from  llifir  jicti\     \'  iii'is' 
M'Is.    Thf  rttliil     'lU'li    >  ti-i. 
siiitouimIs  the  «,  .Is  o' 
serves  as  the  iiiediuin 
|)iiisiiiii.     It  is  the  mid 
the  tissues.     Lympli  is 


h. 


reseliibliiitf  the  hlooi 
the  earryiiij;  itff  o\' 
cial  system  of  vcssi 
walled  caiiill  ti 

hules    li-Jiij    to        ••• 
ulaiid  aloii",'  th( 
sel,  tile  tlioi-aeic     .i 


!•! 


"      ii^t    the    liolll'isllllli'iit 

he  In  :  oduets  whieli 

»  i  iiiolUfh  walls  of  the  m^ 

from  the      pdlaries  and  which 
V  known   .IS  the  lyinpli,  and 
ween  the  cells  and  tli-'  hlood 
iiiije  hetweeii  the  hkuxl  and 
transparent  fluid,  closely 
h  it  is  derive<l.  .  To  aid  in 
vi'e>      !  ,>h.  there  is  piovided  a  s(»e- 

ied  1.  I  niphatics.  which  are  very  thin- 
!  icd  with  endothelial  cells.  These  tu- 
vhich,  after  passinj;  through  a  'ymidi 
i  ,  tinallv  empty  into  a  lar>je  vcindike  vcs- 
lyinjr  alongside  of  the  o-sophaKUs  in  the 
thorax,  and  emptyinff  into  tlie  left  suhclavi.in  vein.  A  smaller 
lymphatic  vesse'  the  liirht  thofacic  duct,  empties  into  the  rifiht 
subclavian  \   in 

The  lynipi    nl         I'd  from  the  thoracic  duct  hy  mrans  of  a  tine 
tube  in.scrte.  •  the  vcs.scl  v;  lic-  somewhat  in  nature.     After  a 

meal  the  fluid  is  like  ndlk.  heeanse  of  the  preschcc  of  droplets  of 
fat  which  have  Ineii  alt-or])ed  from  th"  intestines.  The  lymphatics 
of  the  viscera  appear  as  white  lines  in  th^  mesentery  and  on  thi.s 
account  are  called  lacteaK  The  h  inph  whic  is  collected  dnrin^r 
a  fast  is  vt'-y  much  like  the  Idood  plasma.  It^  spe4-itic  uiavity  u 
less  thtui  tliat  of  blood,  s'lice  it  oiitains  less  protein  ina;(  rial,  hut 
on  the  athi^^  hand  its  salt  content  is  the  same  and  it  •  ot.i  in  much 
th'-   vinii  iui-r  as     lood.     On   microscopic  examinatioii  there 

ai'  !oun<l  inanv  colorlo-  coriniscles.  identical  to  those  i)resent 
m  blood.     iSome  of  Ihese  >    m  jiiuseles  ace  hii   in   1  vvitimi  I;ie  lyiiiph 

156 


g 


!,-)(; 


I'IIYSIOI,Otiy    FOR    DENTAL   STIDKNTS. 


glands  throufjli  which  tlic  lymph  vcssols  pass  on  their  way  to  tiic 
subclavian  vein. 

Lymph  Formation. —Many  physiologists  have  allcniptcd  to 
discover  the  j)reeise  mechanism  by  which  the  plasma  passes 
tiirough  the  capillary  walls  into  the  lyinpii  spaces,  but  the  com- 
l»lete  knowledfje  of  the  process  is  not  yet  at  hand.  The  relatively 
high  blood  pres.sure  within  the  capillaries  provides  filtration 
l)re.ssure  by  which  a  fluid  might  be  filtered  through  the  cai)illary 
walls,  and  there  is  no  doubt  that  such  a  j)rocess  does  occur,  as,  for 
I'xample,  after  the  capillary  pressure  has  been  increased  by  con- 
striction of  the  veins  by  a  bandage,  etc.  Filtration,  howevei', 
cannot  explain  all  the  known  phenomena  of  lymph  formation. 
Osmosis  (p.  27)  also  plays  a  part  as  follows:  The  tissues  use  up 
the  initritional  elements  brought  to  them  by  the  lymph.  The 
diffusion  pressure  of  the  substances  in  the  lymph  is  now  reduced 
so  that  it  becomes  less  than  that  present  in  the  blootl.  Therefore 
substances  within  the  blood  must  pass  out  through  the  papillary 
walls  into  the  lymph,  thus  keeping  the  concentration  of  the  fluid 
more  or  less  constant.  The  waste  products  of  the  tissue  pass  into 
the  lymi>h  and,  by  increasing  the  molecular  concentration  of  the 
lymph,  draw  water  from  the  blood.  Again,  the  breaking  down  of 
the  large  protein  molecules  into  smaller  ones,  in  the  processes  of 
ti.ssue  metaboli.sm.  will  cause  the  molecular  concentration  of  the 
tissues  to  rise,  increasing  the  osmotic  pressure.  This  causes  water 
to  be  abstracted  from  the  lymph,  which  in  turn  draws  on  the 
blood  for  water. 

Lymphagogues. — There  are  certain  substances  which  afTect 
the  rate  of  lymph  formation  in  a  very  peculiar  way.  These  are 
called  lyniphagogues,  and  include  extractvS  from  many  shell  fish, 
leich  extract,  peptones,  etc.  When  such  substances  are  injected 
into  the  blood  of  an  aninud,  there  follows  a  great  increase  in  the 
rate  of  lynsph  formation  and  lymph  flow.  Indeed  some  people 
are  very  su.sceptible  to  this  action,  and  eating  sh<'!l  fish,  oysters, 
and  some  fruits  will  cause  their  tis.sues  to  become  swollen  be- 
cause of  an  increased  lym|>h  formation.  How  these  substances 
can  etVect  the  change  by  altering  the  physico-chemical  con.stitu- 
tion  of  the  blood  plasma  is  not  clear.    Some  investigators  believe 


ii 


THE  LYMPH. 


157 


thiit  tlit'V  liavc  a  stimiilatiiifj  action  on  tlic  cndotliclial  cells  linintr 
Die  cai)illarics  and  tlnis  jjrotlucc  an  actnal  secretion  of  lynipii. 
It  is  more  jn-olmble,  however,  that  they  i)oison  these  cells  in  a 
way  which  increases  their  i)enneal)ility  and  tlius  jn'rinits  a  freer 
filtration  of  lymph  from  the  blood  i)lasma.  There  arc  other 
facts  nevertheless  which  sui)port  the  theory  of  an  actual  secretins 
mechanism  within  the  cells  of  the  capillary  walls,  but  they  are 
t(Ki  technical  to  considei-  here.  They  suggest  that  although  the 
j)liysico-chemi('al  laws  of  dilTusion,  osmosis,  filtration,  etc..  i>lay 
the  most  impoitant  role  in  lynij)!!  formation,  the  cells  of  the 
capillary  walls  may  them.selvcs  have  an  active  i)art  in  the  pro- 
cess. 

Lymph  Reabsorption. — Within  the  tissue  spaces,  and  within 
the  cells  of  the  tissues,  chancres  are  continually  taking  place  which 
alter  the  character  of  the  lymph.  ().\yj?en  and  food  substances 
are  I'emoved  from  the  lymph  by  the  tissue  cells,  and  waste  sub- 
stances, the  result  of  the  ti.s.sue  metabolism,  are  added  to  it.  In 
the  case  of  o.xygen  and  carbon  dioxide,  the  exchange  is  so  reg- 
ulated as  to  keep  constant  the  supply  of  thcst;  bodies  in  the 
lymph.  The  loss  of  any  substance  is  (|uickly  compensated  for  by 
the  addition  of  new  material  from  the  blood.  The  solid  waste 
jnat...r  excreted  by  the  cell  can  also  find  its  way  directly  from 
the  cell  through  the  lymph  and  into  the  blood  plasnui.  It  is 
probable  that  during  i)eriods  of  rest  or  of  slight  activity  the 
lymi)hatics  are  of  little  importance  in  the  exchange  of  the  lymph. 
However,  when  the  exudation  of  lyiui>h  becomes  increased,  as 
during  exercise  or  following  the  use  of  some  lymphagogue.  or 
when  there  are  substances  in  the  lymph  which  the  capillaries 
cannot  absorb  into  the  blood,  the  lymphatics  become  very  im- 
portant in  helping  to  renu)ve  the  excess  of  lymph  formed. 

The  Movement  of  the  Lymph. — The  mechanism  by  which  the 
lymph  of  the  tissues  is  collected  l).v  the  capillaries  of  the  lymph- 
atic system  is  not  understood  any  better  than  the  mechanism  of 
lymph  fornuition,  but  no  doubt  the  same  laws  apply  to  both  pro- 
cesses. The  movement  of  the  lymph  along  the  lymphatic  vessels 
is  ])o.ssible  because  of  the  presence  of  valves  along  the  course  of 
the  vessels. 


158 


PHYSIOUXSY   FOB   DENTAL   STIDEXTS. 


Tlu"  prot'oss  <»f  lyinpli  absorption  is  ratlici-  slow  except  wlioii  it 
IS  anlt'd  by  tii,-  !iiassiij;f  produced  Uy  tli.-  iiioveineiits  of  tlie  siir- 
roundini;  parts.     Tlie  rapid  action  of  poisons,  or  .Irugs  intro- 
duced by  a  hypodermic  syringe,  is  due  to  their  absorption  from 
the  intra-cellular  or  lymph  spaces  directly  into  the  blood.     Col- 
ored solutions  as  india  ink  are  absorbe.l  by  the  lymphatics,  and 
by  using  a  substance  like  this  it  is  i)ossible  to  trace  the  lymphat- 
ics of  a  portion  of  the  body.    Micro-organisms,  such  as  the  strep- 
tococcus, which  causes  one  of  the  familiar  forms  of  what  is  known 
as  blood  i)oisoning.  are  taken  up  by  the  lymphatics,  and  it  is 
••asy  to  ti-ace  the  channels  traversed  by  the  organism  by  the  in- 
flamed lymphatic  wails  which  appear  as  red  lines  under 'the  skin. 
Since  all  these  vessels  pa.ss  through  a  lymphatic  gland  on  their 
way  to  the  subclavian  vein,  these  glaiuls  are  often  very  much 
swollen,  and  may  even  l)e  destroyed  as  the  result  of  the  infection. 
It  is  probable  that  one  of  th,-  functions  of  the  lymph  gland  is  to 
catch  an(]  render  non-to.\ic.  poi.sons  which  are  being  carried  into 
the  circ  .:;   ion  by  way   of  tiie  lymphatics.     One  of  the  most 
dreailed  diseases,  carcinoma,  is  carried  by  the  lymphatic  svsteni 
to  other  parts  of  the  body.    For  this  reason  we  most  often  see  the 
metastatic  growths  of  canc-r  in  the  region  of  the  lymph  glands 
which  have  caught  the  straying  cancer  cell  and  have  been  infect- 
ed by  it. 

The  increased  exudation  (f  lym{)h  in  the  tissu.  ■  .  !i  -h  occurs 
in  inflammatory  conditions  is  n;.  doubt  of  great  ad,  lage  to  the 
tissues,  since,  by  this  mean.s.  a  gr.'ater  sui)ply  of  nourishment  is 
provided  for  the  repair  of  the  damaged  celLs,  and  the  defensive 
substances  (antibodies,  etc.)  are  brought  into  play. 


11*5 


KIk.  14. — DiuKram  of  ("iroulatioii.  Tlip  l>loo(l  ciiculatps  iis  follows:  V.C. 
y.C.  (VfTiiP  cava"),  K.A.  <  ilifht  auricli-).  It.V.  (liBht  Vfntiiclc).  /'.  .1.  (pul- 
monary artery ),  I,. A.  (left  auiiclf).  /,.r.  (left  vt-ntrlcli' ),  .1..1.  and  D.A. 
lascenJinK  and  drscendinK  aorta).  //.  l".  and  /*.  (caiiillariis  of  head,  visc.-ra 
and  lK)dy  Benerally).  I'.V.  (portal  vein).  I.i.  (liver).  The  small  blai'k  ves- 
sels   an-    the    azyj;iis    veins. 


'■ 


CHAPTER  XVllI. 
THE  cniCrLATOKV  SYSTEM. 

Introduction. — Tlic  circulHtory  systom  provides  for  the  trans- 
])ortation  of  blood  through  the  tissues,  thus  euabling  eaeli  indi- 
vidual cell  to  obtain  nourishment  and  to  rid  itself  of  the  waste 
produets  of  its  activity.  The  system  includes  the  heart,  the 
blood  ves-sels,  and  the  lymphatics. 

From  a  mechanical  standpoint,  we  may  say  that  the  heart  con- 
sists of  a  pair  of  pumps;  each  pump  consi.sting  of  two  parts,  an 
upper  dmmber,  the  aiiriclr,  and  the  lower  one,  t!ie  rnitriclr. 
Tiiin.  nuMubranous  valves,  called  aurieido-ventricuiar.  .separate 
the  upper  and  lower  chambers  and  prevent  the  blood  from  flow- 
ing back  into  Hie  auricle  when  the  ventricle  contracts.  Connect- 
ed with  the  ventricles  are  the  nrtcrua,  which  conduct  the  blood 
away  from  the  heart,  to  which  it  is  returned  by  the  great  veins 
leading  into  the  auricles.  At  the  point  where  the  arteries  emerge 
from  the  heart  are  cup-shaped  valves,  called  8(Mnilunar,  which 
])revent  the  passage  of  blood  from  the  arteries  into  the  ventricles, 
while  the  latter  are  relaxing. 

As  will  be  seen  from  the  accompanying  diagram  (Fig.  14)  the 
blood  pumped  from  the  two  sides  of  the  heart  circulates  through 
two  distinct  and  separate  systems  of  blood  vessels.  From  the 
right  ventricle  the  blooil  goes  through  the  pulmonary  artery  to 
tht>  lungs  and  is  returned  to  the  left  auricle  by  the  pulmonary 
veins,  then  to  the  left  ventricle,  whence  it  is  sent  over  the  body 
through  the  aorta  and  its  branches,  to  the  <'apillaries  imbedded 
in  the  tissues.  From  these  it  is  returned  through  the  veins  to  the 
venjB  cavae,  which  discharge  it  into  the  right  auricle.  We  may 
.say,  therefore,  that  the  circulatory  system  consists  of  two  circles 
of  tubing  interposed  in  which  are  two  force  pumps,  the  valves 
of  which  are  so  disposed  as  to  allow  the  blood  to  flow  in  one  direc- 
tion only. 

150 


KiO 


l'IIYs|nI,0(iY    Filli    OKNTAt;    STIOIATS. 


I.    The  Heart. 

Anatomical  Considerations.  —Tin-  licart  is  suspciKicd  at  its 
base  by  tlic  lar<;c  arti'i-ics.  and  lies  practically  free  in  a  sac  of 
toiiffli  fibrous  tissue  called  tlic  /><  riitinliinn.  On  cadi  side  arc  the 
lun<rs.  witli  the  diai)hrafriii  below,  the  chest  wall  in  front,  and  the 
lesopiiafTUs  behind.  (  Ki^r.  1.') ).  The  surface  of  the  heart  and  the 
interior  of  the  pericaidial  sac  are  bathed  with  a  serous  fluid,  the 
pericardial  lluid.  The  muscular  fibers  forniinf;  the  walls  of  the 
four  chaiidters  of  the  heart  are  arranjjed  so  that  their  contrac- 


I-"rjr.    l.'>. — Thi'   iM.sitii.ii  i>r  t:.c   hcail    in   !V,i'   t!..iriix.    i  T.    WiriRMlf  TmlcM 


tion  diminishes  the  size  of  the  cavities  and  empties  the  heart  of 
bi(Mid. 

From  the  study  of  the  eiid)ryonic  heart,  and  from  comparative 
studies  in  the  lower  animals.  (  Kiir.  16)  we  know  that  the  h"art 
has  develo|ied  from  a  sinj^le  tube,  the  division  of  the  auricles  and 
the  ventricles  Inmu^j  a  rather  lat.  sta<je  in  the  development  of  the 
mammalian  heart.  The  fact  that  the  two  auricles  beat  syiicliro- 
nously.  followiMJ  by  the  contraction  of  the  two  ventricles,  is  sifrni- 
ficant  of  the  dcvel->p!neiit  of  the  auricles  from  the  proximal,  and 


r»   — -  -  .'  —i^    .   .^-  i-"^'_wi  I 


^TTT^Bi!* 


ANATOMY    (IK   Till:    IlKAKT. 


Kil 


of  till'  ventricles  from  the  distal  end  of  tiie  |)rimitive  eardiic 
tube. 

The  fibers  of  the  auricles  run  transversely,  hetriiniinji;  and  end- 
ing in  the  fibrous  tissue  which  separates  the  aui'icles  from  the 
ventricles.  The  musculat\ire  of  the  veiitriclcs  is  somewhat  hard- 
er to  trace.  There  are  layers  that  run  transversely  around  the 
ventricles,  and  also  layers  which  describe  more  or  less  of  a  spiral 
course  from  the  base  of  the  ventricles  to  the  a|)ex  and  then  are 
reflected  back  in  transverse  layers,  until  they  finally  end  in  the 
papillary  nniscles,  which  are  connected  with  fibrinous  threads. 


yifi,  ifi._A  K'lniializiii  \  iiw  cif  tlir  viMtcliiiitf  licait  (Kt-ith)  sliowinn:  ((. 
the  sitniw  mmiipsus;  Ii.i-.,  tin-  iiuiiclf  ;  .!.(.  the  auiiculo-VHiitiiculiir  niilkc  and 
valVfM-,  (/.  tiK  rinlrich- :  c.  thi>  IwRinninp  of  tlit-  aof.ii  with  the  sciniluiiai- 
valves  at  .'..  The  valves  lietweeii  <  anil  /  <Ii>  nut  exist  in  the  heart  of  inati. 
(Kicini  liMWell's  I'h.v«lol<iKy.) 

the   chorda-   tendinca".   to   the  edge   of  the   auriculo-ventricular 
valves. 

When  the  ventricles  contract,  this  arrangement  of  muscular 
fibers  causes  the  ajie.v  am!  the  has*-  of  the  heart  to  ai)proach  one 
another,  and  the  transverse  .section  is  changed  from  an  ollip.se  to 
a  circle.  The  ba.se  of  the  heart,  hung  as  it  is  to  the  large  vessels 
ill  the  thora.x.  appears  to  be  fixed,  and  one  would  expect  that  the 
apex  is  the  part  which  move»  up  and  down.    This  is  not  the  casi'. 


^^s^^m- 


I(i2 


1'llYSlUl.lKiY    KOli    l)i:\TAL    STIDKNTS. 


liowi'vcr.  .as  is  shown  by  «'X|>(i'iiiii'iit.  iiiul  is  cxjdiiiiHMl  by  tlu-  fact 
that  the  blood,  when  it  is  forced  from  •  ventricle  during  the 
cardiac  contraction,  exerts  its  force  on  tlic  apex  as  well  as  on  t'.'f 
blood  in  the  arteries.  This  serves  to  fix  the  apex  in  the  vertical 
])ositioii  and  to  bi-ing  the  base  of  the  ventricles  downwards 
during  their  contraction.  In  some  individuals  there  is  a 
vi.sible  pulsation  at  about  the  level  of  the  fifth  rib  on  the  left  side. 
This  is  called  the  apir  huif,  and  is  caused  by  the  rotation  of  the 
apex  in  the  transverse  diamet«'r  and  by  the  sudden  chaiiK*'  (tf  the 
ventricle  from  a  soft  flabbv  condition  into  a  firm  one. 


i4.~  1 


Fin.  1". — KiuKram  of  Valve.s  (if  tbe  Hf.i  '  The  valves  are  .mipiio.seil  to  l>e 
viewed  from  above,  the  aurieleK  havinir  l«en  iiaitiall.v  leinoveil.  A.  aorta 
with  semilunar  valve:  H.  pulmonar.v  artery  anil  valve;  (\  trii  iisplil,  and  T>. 
mitral  valve;  A'.  riKht.  and  F,  left  coronary  artery;  (r,  wall  oi  liKht.  and  //. 
oi  left  aurii'le :  /.  wall  of  right,  and  •/,  i..  left  ventriele.  (  Kroni  .Stewarts 
rhysiology. ) 


11 


The  walls  of  the  auricles  are  relatively  thin,  as  they  are  not 
reijuired  to  do  heavy  work.  The  ventricular  muscles,  on  the 
other  hand,  are  well  develoj)e(l.  that  of  the  left  ventricle  being 
very  strong  and  adapted  to  the  heavv  work  it  must  perform. 

The  valves  guarding  the  opening  between  the  "iricies  and 
ventricles  are  eomposed  of  thin  membranes  of  fil»rous  tissue,  cov- 
ered with  endothelial  cells  similar  to  the  lining  of  the  heart  and 
the  blood  vessels  (Fig.  17).  In  acute  rheumatism  and  tonsil- 
litis, the  endothelial  covering  of  the  interior  of  the  heart  and  of 
the  valves  is  often  inllamed,  and  permanent  changes  may  take 


TIIK   lll'.AKT   HKAT 


163 


|»lac»'  wliicli  iii,j\irp  tlu'  valves  aiul  jirodnt't'  what  is  known  as  val- 
vular dist-asc  of  tlic  heart.  The  chorda'  tendinea'  connect  the 
free  nnir>?iiis  of  the  valves  with  the  i>a|)illary  muscles,  which  ariso 
from  tin-  musculature  of  the  ventricle  like  little  knobs  of  tissue. 
This  arrangement  jjpevents  the  valves  from  being  everti'd  into 
the  auricle  during  the  contraction  of  the  ventricle.  The  valves 
on  the  left  side  consist  of  two  flaps  and  are  called  the  uiitnil 
rolffs;  those  on  the  right  side  have  three  flaps  and  hence  are 
called  tricuspid  valve.s.  The  valves  guarding  the  arterial  orifices 
consist  of  three  cup-shaped  niend)ranes  and  are  known  as  the 
s(  mil(it\itr  vdlrrs,  because  of  their  crescent-shape  when  they  are 
closed.  Whenever  the  i)ressure  in  the  arteries  is  greatei-  than 
that  in  the  ventricles,  these  valves  are  tigiitly  closed,  and  i)revent 
any  blocxl  entering  the  ventricle  from  the  arteries. 

The  Physiologic  Properties  of  Heart  Muscle. 

The  Character  of  Cardiac  Contraction.— The  contraction  of 
our  voluntary  nniscjes  is  not  due  to  a  single  stimulus  sent  from 
the  brain  through  the  nerves,  but  rather  to  a  series  of  such  stim- 
uli, which  ])roduce  a  nu)re  or  less  continued  or  tonic  contraction 
of  the  muscle.  If  this  were  not  the  case,  our  movements  would 
l)e  very  (piick  and  .jerky,  similar  to  those  nuule  by  <■  son  suf- 
fering with  St.  Vitus  dance.  In  the  case  of  the  lit....  nuisde, 
however,  each  l)cat  consists  of  a  single  complete  muscular  con- 
traction, and  it  is  impassible  to  prwluco  a  tonic  or  continued  con- 
traction in  the  lieai't  such  as  can  be  produced  in  voluntary  mus- 
cle by  rapid  successive  stimuli.  Another  peculiarity  of  heart 
nuiscle  is  that  each  time  it  contracts  it  does  so  with  all  the  force 
that  it  has  at  the  moment.  Skeletal  mu.scle  contracts  with  great- 
er or  less  intensity  according  to  the  strciigth  of  the  stimulus  it 
receives. 

Heart  muscle,  and  in  a  lesser  degree  some  other  muscles,  such 
as  those  of  the  intestinal  tract  and  splwn.  have  the  power  of 
making  autonuitic  rh\  thmic  contractions  which  follow  each  other 
in  a  definite  senuence.  Thi.s  phencmienon  in  the  case  of  cardiac 
muscle  is  not  dependent  on  the  influence  of  the  nerves,  as  can  be 
sLawu  bv  the  fact  that  the  heart  removed  from  the  body  will  con- 


■^,-.  .«*'■ 


.:;,'■- 


Trrr^^'fsmm 


1(14 


i'iivsr(ir,iMiv  K(ii{  i)i;\T\i,  stidknts. 


tiniif  to  Ix'Ht  for  sonif  time  if  it  is  |»ro|Mrly  iiourislicd  hy  perfus- 
ing' hlooil  Ihroiif,'!)  it  uihIiT  iucshuic.  TIh'  cause  of  this  piop- 
•Tty  of  aiitoniiitieity  is  still  unsettleil.  ami  there  have  hi  eii  some 
very  iiiterestinjr  (iiseiissioiis  iiixi  arjfumeiits  amoiiff  physiologists 
eoneeriiiiiff  it.  Some  iH'lieve  that  tiie  heart  miisele  has  this  prop- 
erty inherent  in  itself,  and  that  it  ori>rinates  the  impulse  which 
causes  the  contraction  of  the  heart;  while  others  think  that  there 
are  pres«'nt  in  the  In  an -muscle  cells  of  a  nervous  character  whose 
special  function  it  is  to  orifjinate  the  heat.  Kxperimeiital  facts 
can  1m'  found  in  siip|)ort  of  «'ither  theory,  hut  the  (|uestion  is  still 
in  dispute.  Heart  muscle  dirt'ers  from  nthi-r  mu.scle  in  that  each 
Hher  consi.sts  ttf  a  single  cell  containing  striated  |H'otoplasm.  It 
imiy  (|uite  well  be  that  this  kind  of  muscle  pos.se.s.ses  some  char- 
acteristics usually  a.scrihed  to  nervous  ti.ssue,  and  that  it  does 
orijrinate  the  stimuli  which  produce  automatic  movements. 

The  Sequence  of  the  Heart  Beat. — Inspection  of  the  heatini; 
heart  of  a  recently  killed  turtle  or  frojf  shows  that  the  heart  heat 
hejjins  hy  a  contraction  in  the  lartre  veins  where  the.v  .join  the 
auricles.  From  these  vessels  the  heat  spreads,  as  it  were,  to  the 
auricles  and  then  to  the  ventricles,  iM-jjinniiiff  at  the  base  and 
ending  at  the  apex.  It  is  possible  to  stop  the  contraction  of  the 
ventricles  by  drawiufj  a  threatl  tightly  around  the  heart  between 
the  aurich's  and  the  ventricles.  The  aur  -les  will  contiiuie  to 
beat  as  before,  and  the  ventricles  can  lie  mad  to  beat  rhythmical- 
ly again  by  artificially  stimulating  them.  In  this  case,  how- 
ever, they  will  contract  without  any  reference  to  the  aiiricidar 
Ihat.  Likewise  the  base  of  the  large  veins,  or  the  sinus  venosus 
as  this  is  known  iu  the  aini)hibian  heart,  ma.v  be  separated  from 
the  auricles  hy  a  tight  thread.  The  auricles  now  continue  to 
beat,  but  at  ;i  much  slower  rate,  whereas  the  beat  of  the  sinus 
is  not  changed.  Tin'  tissues  of  the  sinus  mu.st  pos.sess  to  a 
marked  d'gree  the  power  of  making  individual  or  automatic 
movements ;  they  are  thus  able  to  control  the  rate  of  the  heart. 
For  this  reason  the  sinus  has  been  called  the  tnrdittc  piuemitkrr. 

The  great  muscular  development  of  tlie  human  heart  has 
caused  it  to  lose  some  of  its  })rimitive  characteristics.  Xeverthe- 
k'ss,  there  still  exist  in  the  musculature  of  the  heart  some  strands 


aS" 


Till-:    IIKAItT    HKAT 


163 


of  tissue  wllicll  ns*  lulitc  tln'  tissue  of  the  ievs  ilevclopetl  tir  more 
piiinitivi-  lieait.  We  (iiid  in  the  Wiills  of  the  aiirieies  siiiHii  nodes 
iiiid  islets  of  tissue,  whieli  no  iloiilit  represent  the  sinus  tissui's 
found  in  the  frojjs  heart.     These  nodes  of  tissue  are  really  the 

pacemakers  of  the  heart,  for  it  is  in  them  that  the  impiils • 

stimidus  arises  whieh  sets  anoin>.'  tlu'  contraction  of  the  auricles 
and  the  ventricles.  These  nodes  are  connected  In  fibers  with  the 
musculature  of  the  auiides  and  ventricles,  those  runiiinjr  from 


Vijr.  IS.— Dissfilioii  i.r  tifuit  ti(  xliow  nuilful.)-v<iitiiiulitr  l.uiiiUf  iK.itli)  ; 
.(.  thi-  iK'KinniiiK  of  llif  tuiiullr.  known  n.x  thr  .\-V  noilc  ;  ,'.  Ih.-  Ipumnr  .lividinK 
Into  two  liiancliis  ;  1,  ttif  l)ian<ti  lunniiiK  on  tin  liK'lit  sUU-  of  the  inttrviii- 
ti-lcular    .stiitum.       i  Kroin    How.U'.s    l'li>  sioloK.v. ) 

the  auricles  to  the  veiiti'icMS  lu'lnj.'  •rathered  into  a  hundle  of  ti.s- 
siu-  which  has  been  named  the  hinulli  of  Ilix  (!''!>.'.  H). 

Numerous  eases  have  been  recorded  of  iiulividuals  liavinjr  a 
very  irregular  or  a  very  slow  heart  In-at  in  whom  post-mortem 
examination  of  the  heart  showed  a  diseased  condition  of  the 
bundle  of  His.  The  conditions  oliserved  in  man  have  been  re- 
l)roduced  in  the  case  of  animals  by  cuttinj;  or  clamping  the  tis- 
sue about  this  binidle.  The  result  is  much  the  same  as  that  ob- 
served ill  the  turtle's  heart  when  the  striii}.'  is  tied  between  the 
auricle  and  the  ventricle.  The  ventricle  may  continue  to  Iteat. 
hut  it  does  so  without  reference  to  the  aiu-icles.  Such  a  condi- 
tion is  known  as  luarl  block. 


166 


I'UVSIOUKIV   Ft»B  IlKNTAL  STtDENTH. 


It  is  of  iiifcrcHf  to  know  tluit  tlitTc  )ih.s  hccii  <|iiit('  iiii  ailvaiicc 
n-cfiitl.v  ill  tlu'  kiiowlctlK*'  of  the  foiMluctioii  of  tlic  cardiac  iiii- 
pulst'  from  the  auridcM  on  to  the  ventricles.  It  has  been  known 
for  a  hniff  timi'  that  when  a  imiscic  contniets.  a  small  but  definite 
el. 'trie  current  is  set  up  iK-tweeii  the  relaxed  and  the  contraet- 
injf  portions  of  the  muscles.  New  methods  of  detecting  and  rc- 
eordiiiK  the  direction  of  the  flow  of  .such  currents  produced  in 
the  heart  in  man  have  shown  that  cases  of  heart  block  are  by  no 
means  rare.  The  instrument  used  for  this  puipos*-  is  a  'lighly 
sensitized  galvanom.  ler.  and  the  tracinjrs  arc  known  as  r/.  Iru- 
(iinlioi/rattis.  \\y  this  method  it  can  br  shown  that  in  certain 
eases  of  iieart  disease  the  auricles  beat  twice  to  the  ventricles 
once,  or  a^ain  that  the  auricles  may  boat  very  fast  vhile  th<' 
ventricles  arc  beating  very  irrcfrulariy  and  slowly. 

The  Action  of  Inorganic  Baits  on  the  Heart  Beat.— A  very 
interestinp  theory  has  recently  been  advanced  concerning  the 
cause  of  the  heart  beat.  It  will  lie  remembered  that  the  niood 
contains  salts  of  .scxlium.  pota.ssium  and  calcium  in  solution.  If 
these  salts  are  replaced  by  other  non-poi.sonous  .salts  in  the  same 
concentration  as  the  .salts  removed,  the  heart  will  not  beat.  If 
the  heart  is  perfu.sed  with  a  .solution  of  sodium  chloride  aloiic. 
the  beat  becomes  very  weak  and  finally  stojjs.  If.  however,  a 
small  amount  of  calcium' and  potassium  salts  is  aibh-d  to  the 
sodium  chloride  solution,  the  heart  will  again  begin  to  beat,  but  it 
stops  after  a  while  in  a  state  of  rela.xation.  or  diastole,  if  calcium 
chloride  is  removed  from  the  solutiun,  or  in  systole,  or  contrac- 
tion, if  the  potassium  .salts  are  removed.  These  experiments  sug- 
gest that  the  salts  of  the  blood  otr.-r  a  solution  to  the  problem  of 
the  eau.se  of  the  heart  beat,  the  potas,sium  favoring  relaxation, 
and  the  calcium  contraction.  If  the  proper  balance  of  tlie.se 
salts  is  present  in  the  blood,  it  is  conceivable  that  a  regular  se- 
(juence  of  contraction  and  relaxation  of  cardiac  muscle  will  take 
place  because  of  the  action  of  the  .salts. 

The  Vascular  Mechanism  of  the  Heart. 

Definition  of  Terms.— A  definition  of  the  terms  !ii»plied  to 
the  different  phases  of  the  heart's  activity  will  help  in  the  tie- 


Tin.    (.\1C0IA<-   CYCIJ 


lf)7 


s<'ri|ifi((ii  lit"  tl vnits  wliidi  dciMir  ilui-in>^'  tin.'  <-iim|.|.ti'  li.art 

l)ciit.     The  iMTidd  ol'  ai'lunl  cuntnictiini   c>t'  tli<'  Ikjii-I    is  ti-r li 

st/sloh .  This  is  tlividnl  into  mirli  idtir  inn!  ii  ulni  nhir  siixlith  . 
The  term  sfilnii/mli  jii  rioil  is  itpplicd  t(»  that  |)art  ot'  vriitriciilar 
svstolf  (luriiitf  which  thf  IiIinmI  is  ac-ttially  h-aviiij?  tlir  vcntiifl^s. 
Th<'  iM'i'iod  of  n-laxatioii  ami  n-st  ot"  the  i-anliac  imis<'h-s  is  callfl 
iliustiilr.  Thf  iiirdiiii  (  i/ili  iiii'lii.h's  tin-  tiim-  of  systole  an. I  ilias 
tolf  of  the  licart. 

The  Events  of  the  Cardiac  Cycle.  -During  iliastoh  tiir  1>Ioim1 
f<t\-  ill  a  steady  stream  from  tli.  uifat  veins  throii^jh  the  two 
,,!ir>.  ies  :,,'(•  the  veiitrieles.  the  aniii'uhi  vent ricnhir  valves  hi-iin: 
,,|  ;  .,  \\1h-\  the  Veiitrieles  are  as  full  as  the  wriyht  im!  the  pres- 
s-.r  (  (  I).  ■  hlooil  eaii  make  theiii.  aiirieiilar  :-.-  'ole  liejrins.  The 
.  ;  ;  :u  \ .iitrieiilar  valves  at  this  instant  are  Hoatiiitf  in  the 
hlonc'i  which  has  colle<-te(l  in  the  ventricles,  and  are  almost  in  the 
jiosition  of  elosiirc.  hnt  a  narrow  chiiiK  still  remains  hetweeii 
them,  and  throujrh  this,  anriciilar  svstole  fon-'/s  blood  under 
pressure  into  the  ventricle,  thus  fillin>r  tin  ventricles  eompletely. 
At  the  tlead  stop  of  aiirieulnr  systole  the  le  are  currents  of  Mood 
rcHcctcd  back  alonj?  the  sides  of  the  ventricles  which  strike  the 
i.inder  surface  of  the  valves  and  comi)li-tely  clos.-  them.  Ven- 
tricular systole  now  iM^ins.  The  closed  valves  prevent  tlx'  pass- 
ajre  of  blood  back  into  the  auricles,  and  the  entire  force  of  the 
ventricles  is  expeixled  in  forcing:  the  blood  out  through  the  ar- 
terial o|)eiiiiiKs.  Whenever  the  pressure  in  the  ventricles  cxcceiis 
that  ill  the  arteries,  the  .semilunar  valves  open  and  remain  ojicn 
till  the  force  of  the  ventricle  falls  below  the  pressure  of  blood  in 
the  arteries.  The  time  between  the  dosing  of  the  auriculo-veii 
tricular  valves  and  the  openinj.'  of  the  semilunar  valves  is  calhM' 
the  period  of  <ietting  up  power,  or  the  /</v  -sphiiffmii  pi  rin-l  (  Fifi. 

1!)). 

It  is  obvious  that  when  tin-  blood  is  leaving;  the  veiitr.cles  the 
pressure  must  be  les.s  in  the  arteries  than  in  the  heart.  Kacli  ven- 
tricle pcmrs  out  more  blood  into  its  artery  than  can  pass  throiiKli 
the  capillaries  in  the  same  unit  of  time,  and  hence  the  arterial 
walls  are  stretched  and  the  blood  is  put  under  their  elastic  ten- 
sion.    At  the  moment  the  ventricles  exert  less  pressure  than  does 


T!53 


1(J8 


l'IIYSI(>l,(MiY    K(l|{    DKNTAI,    STIDKNTS. 


ll'  S<'llliluiliir  Villv 


the  clastic  recoil  of  tlic  iirtcrics  on  tlic  hlood.  the  wiiiiiuiiar  valves 
arc  dosed  tifflitly  by  backward  cddyiiifr  currents  in  tlic  arteries. 
Their  closure  j)revents  any  return  of  blood  into  the  ventricles. 

The  bloml,  having  attained  a  certain  inonieiituin  (lurinj?  the 
sphyjjniic  period,  is  carried  ou  by  its  inertia  for  a  fraction  of  a 
second  after  the  ventricle  cea.ses  to  exert  i)ressMre  on  it.  thus  pro- 
ducing a  partially  relaxed  artery  just  beyond  the  sniilunar 
valves.  This  nionientuni  beiuff  lo.st,  the  bloo<l.  by  the  i)ressnr.- 
which  the  stretched   elastic  wall   of  the  arteries  i-xerts  on   the 


Kit;    i:<._l>iiiK.iiiii  Nhc.wiiiK  ivliitive  p: cssur.-  in  tiuiiclc.  vi'iitri.-l..  iiii.l  udrhi 

l)lo()d.  is  forced  back  on  to  the  semilunar  valv.'s  and  into  the  par- 
tially ivlaxed  base  of  the  aorta.  The  blood,  beiiifr  thus  prevent- 
ed from  returnin't  to  the  heart,  n.u.sl  contiiuie  to  How  on  into  the 
capillaries,  and  this  onward  How  never  cea.s<'s.  because  tin  next 
cardiac  systole  occurs  before  the  arteries  have  ceas-d  to  exert 
all  of  their  recoil  pressure  on  the  blood  (see  also  p.  ITlii. 

After  the  arterial  valves  close,  the  ventricles  eontiniie  to  relax, 
and  the  pressure  within  quickly  falls  below  that  whieh  obtain.s 


XT 


TIIK  iii;ai!t  SOr.NDS 


Hi!) 


ill  the  partially  filled  auricles.  At  this  nioiiieiit  tlie  weifjlit  (if  the 
lilood  whieh  has  aceiiiiiulateii  in  the  auricles  diiriii};  the  systole, 
forces  the  valves  of  the  auriciilo-veiitriciilar  orifice  oiieii,  and  the 
ventricle  apiiii  hcirins  to  fill.  The  pei'iod  between  the  closure  of 
tlie  seiiiiluiiar  valves  and  the  opeiiinjjr  of  the  aiiricirio-vciitricular 
valves  is  known  as  the  />a\7-.v/>/i//.7>*(/r  in  ri.xl,  and  is  the  hej^in 
niiifi  of  the  diastole  of  the  ventricles.  The  aliove  events  com- 
prise tliose  takiiif?  jilacc  in  a  coinplete  cardiac  cycle. 

The  Heart  Sounds.— If  one  applies  his  ear  to  the  front  of  the 
chest,  or  lietter  still  uses  a  stethoscope,  which  physicians  use  to 
e.xaniiiie  the  .sounds  of  the  luiifrs  and  heart,  two  sounds  will  lie 
heard  duriiifj  each  cardiac  cycle.  Tlu'  lir^i  somid  is  dull,  low 
pitched,  and  loiifr;  the  second  sharp.  Iiifrh  ami  short.  l<'ollowint? 
the  second  sound  is  a  short  pause.  It  has  lieeii  di'tcriniiied  ex- 
pcriiiieiitallv  that  the  first  sound  is  caused  partly  by  the  closure 
and  sudden  tension  of  the  auriculo-veiiti'icular  valves  at  the  iiio- 
nient  of  eardiac  .systole  and  parll.v  liy  the  inuseiilar  contr:ietion 
f  the  ventricle.  Anythiiifr  which  interferes  with  the  closure  of 
the  valves  causes  an  alteration  in  tin  sound;  for  instance,  if  the 
valves  are  diseased  there  will  lie  a  leakinjr  of  blood  back  into  the 
auricles  dui'injr  systoh'.  and  this  will  cause  a  distinct  niuriiiur  to 
take  the  place  of  the  sound.  If  the  musculature  of  the  heart  is 
\veakeiie<l.  the  sound  is  also  modified.  IlriK-e  ihe  first  sound  of 
the  heai't  is  an  important  diatrnostic  si<fn  in  heart  disease.  The 
second  sound  of  the  heart  is  due  to  the  sudden  tension  e.xerted 
on  the  semilunar  valves  at  the  moim  'it  the  blood  is  forced  back 
(III  them,  followiiitr  veiitri'ular  sy  toh-.  'j'his  sound  is  also  sub- 
,ject  to  vai'iafiotis  in  licai-t  disease,  ■•'specially  in  disease  of  the 
valves  tlieinselves.  in  which  case  iiecause  df  rou;.'heiiin<;  they  may 
offer  resistance  to  the  out  rush  of  blond  I'rom  tin  xcntrielrs.  or  In- 
not  dosintr  titrhtiy,  allow  the  p,issa<re  i'\  blood  in  the  wiMiisr  direc- 
tion, ill  either  case  the  >ouiid  is  eliaiii^ed  in  character  and  is  a 
useful  iliatrnostic  siirn. 

iJy  iisiiitf  these  heart  sounds  as  sijrnals  of  the  events  (M-currin^ 
within  the  heart,  it  is  pnssibh^  to  calculate  the  lime  relations  of 
the  various  phases  of  the  i-,ii'(liai-  cyeii'.  The  heart  in  th"  ordinary 
individual  \x-nU  alimit  seven1\'  times  a  iiiinii'''.  su  that   we  mav 


170 


PHYSIOLOGY   FOR   DENTAL   STUDENTS. 


t  ' 


say  that  tin-  pardiat'  cycle  is  completed  in  about  ono-tcnth  of  a 
second.  Systole  of  the  auricles  takes  about  one-tenth  of  a  second, 
systole  of  the  ventricle  thri'e-tenths  of  a  second,  and  diastole 
al)out  four-tenths  of  a  second. 

Diseases  of  Cardiac  Valves. — If  the  mitral  valve  is  diseased, 
tlie  blood  may  be  retarded  from  tlowing  from  the  auricle  into  the 
ventricle.  This  condition  is  called  mitral  stenosis.  If  the  valves 
cannot  close  ti>rhtly  and  thereby  permit  the  blood  to  regurgitate 
into  the  auricle  during  ventricular  sy.stole,  the  condition  is  called 
mifrnl  intiuffkinici/.  Disea.se  of  the  semilunar  valves  is  likewise 
divided  into  aortic  .stenosis  and  insufficiency,  dejx'iuling  on  the 
ciiaracter  of  the  fuiu-tionai  change  in  the  valves. 


11^ 


('HAPTKU  XIX. 
TIIK  CIWcri.ATION   (C.Hi!  .1 
The  Blood  Flow  Through  the  Vessels. 

Introduction. — A  rlciircr  iilc.i  of  ihc  prin.  iplis  ndvicniwir  tin' 
circulation  of  hlood  tln'oiifjii  tin-  vi-sscis  can  he  luul  it'  tht  laws 
ffovcniiiif?  tile  How  of  watci-  in  a  cit>-  watc-  -ivstcm  arc  callcti  lo 
iiiiiid.  For  c.\aiii|)lc.  a  water  works  system  ^>  ari-aiiu<'ii  hy  iiieans 
of  cither  special  pumps  or  a  staiiii|tipt  to  tiirnisli  a  sti'cam  of 
water  at  constant  rate  and  |)ri'ssnre  into  tin  city  water  mains. 
The  water  is  first  forced  into  one  large  pi]>e  and  from  this  de 
livcrcd  to  the  consumer  hy  means  of  niiicii  smaller  pipes.  \\y 
simple  mathematical  calculation  it  can  li»'  slumwu  that  the  total 
cross-soction  area  of  the  smalh-r  pipes  is  iii;ni\  limes  that  of  the 
main  pi|)e:  for  the  sake  of  arjrument.  let  us  sa.\'  N(}()  times  <rreat- 
er.  Thend'oi'c  the  averai^e  rate  of  flow  of  water  in  the  smallei- 
pij)es  must  he  SOO  times  less  than  in  the  main  pipe.  pro\  idinj;  all 
the  outlets  are  oi)cn.  However,  if  onl\  on. -half  of  the  distrihiil- 
ing  pijx's  arc  in  use.  the  flow  of  w.tter  wonid  he  only  400  times 
less  than  in  the  main  pipe,  and  the  -.•sistance  offered  hy  tiie  walls 
of  the  ])ipes  to  the  tlowinjr  watei-  is  itlwi  iialv.'d.  Thus  lh.  same 
amount  of  water  is  delivei'ei!  m  the  saioie  unit  of  time  hut  undei' 
twice  the  iifevsurc.  since  onl\-  twje-half  <f(  flie  force  used  to  deliv- 
er the  water  through  all  the  pip»i*  w  in*-!'!  in  delivcrinjr  it  tliri>uy;h 
one  half  of  them.  In  otlt^-i-  *»-tkr>'i*.  it  takes  X  I'orce  to  ovci'comc 
the  resistance  offered  l»y  Y.  th'-'M'ore  X  ei|Unls  V.  When  X  re- 
mairiK  constant  and  Y  is  halved,  fh^'ii  X  -V  2  e<f«als  X  'J,  Icav- 
inff  X  2  as  a  fenniinder.  To  hrin<r  it  home,  there  is  less  water 
delivered  from  the  garden  hose  and  it  has  far  i.i*s  pr.ssure  he- 
hind  it  wlien  all  the  nr  -hhors  are  also  usin^r  the  watei-.  tlian 
there  is  when  only  a  few  outlets  are  in  use  Likewise,  if  the 
amount  and  tlie  pressure  of  water  in  the  main  pipe  ari'  varied 
liy  chan(;iri<r  the  force  of  the  puiiip>  or  the  level  of  water  in  the 
stand  pi|>e.  the  amount  of  pressure  of  water  d»'li^''''<'*l  »'>  i'l*«* 
xaried  in  the  same  direction. 

17! 


17l' 


I'llVSlOI.MIiV    K(IH    KHNTAI,    STIDKNTS. 


i 


Th<-  pvHiips  (ir  thf  stiiii(!|.i|)c  corn-spoiK]  t.>  tlic  licart  and  tlic 
lartrc  iirT.rics.  tli.'  disti-ihiiti.nj:  Iii|><'s  to  the  Miiallcr  aHcri.-s  aiul 
«r*apillarr!'s.  Wifli  rlii'sc  idcits  in  m,»i(i  let  us  consider  tin-  i)art  the 
iH'Mrt  iiii.i  bioiMJ  vessels  |il;i\  in  iiiaintainint;  the  eifeidation. 

The  ^rt  the HMUt  Hiys.— At  each  systole  (id  t..  !»o  c.  c.  ot' 
Wwxl  aif  force.,  into  r-hr  aoHa.  Cardiac  systole  lasts  about  ().:! 
♦rf  a -«.co».l.  fhe  diiwtwJe  ()..".  second.  Therefore  the  heart  is  rest- 
vm.  about  (iO  per  cent  of  the  time.  |!y  .'xpcriiiient  it  has  been 
demonstrated  that  th.-  left  vent  ride  forces  the  i)l<)od  out  into  the 

aorta  with  a  presH«:-e  e.|uivaieht  to  the  weji.'h'^  of  i Iiimii  of 

mercury  from  IW)  n,  l!t(»  mm.  in  heifrht.  Th.'  heart  alone,  Innv- 
ever.  actually  propels  the  IiUhmI  through  the  arteries  for  only  the 
t:me  of  its  sysjoie ;  dnrin>r  th-  diastole,  as  alrea.jy  explained,  the 
Mood  wouM  c^Hse  t<.  flow  .■ntirely  if  it  were  not  foi  iie  part 
wliich  the  lara?-  artern-s  plav  in  r\^^.  mainiaininyr  of  the  circula- 
tion. 

Tfe  Part  tke  ansnes  Ray.  -  if  't^ti  >■  r.  .,f  waiii-  are  t..reed 
even  O.S  seciwid  iwo  an  oniiriury  uieral  pipe,  in  0 :;  second.  iDd 
c.  c  mast  flow  ,mt  irmn  rh»-  opposir.-  en.i  in  the  siime  period.  For 
()..'>  M-itmni  no  wat»-r  will  he  tlowini.'  ni  the  Tut«e.  Let  us  iu»w  re- 
place ti=,^  im'taJ  Tul)t-  w,Ti!  ail  eia.stie  nibliee  rube,  riie  end  of  which 
is  fitte<i  with  a  nozzle  rille<i  with  irlasw  \umAH.  If  now  KKt  c.  c.  of 
water  an-  forc.-d  into  The  rube  in  U.:!  s«.cond.  the  niblK-r  tulw  ex- 
pands beeauHc  tIk'  bjeads  retard  tbf  free  outtiow  ..f  water  an.l  thus 
inmn-  it  inipo-ssible  for  100  e.  c.  of  water  t(»  pass  throuirli  them  in 
the  time  alloted.  After  the  water  ceases  to  flow  into  th--  tube,  the 
wafer  stored  'ip  in  the  .'xpanded  portion  continues  to  flow  out 
fhroiifrli  till  beads  because  of  the  elastic  recoil  of  the  rubber.  If 
the  resistance  otl'ered  to  the  water  and  the  expansile  force  of  the 
tube  be  properly  ad.ju.sted.  a  constant  stream  of  water  may  be 
obtained  fr.)iii  the  outlet,  in  spite  of  the  fact  that  an  interiiiitteiit 
force  is  supply injf  the  water  (  Fi^r.  -Oi. 

The  intermittent  stream  of  the  arteries  is  ehan<reil  into  the 
eon.stant  stream  in  the  veins  by  a  somewhat  simdar  process.  The 
walls  of  t!ie  arieries  are  composed  in  part  of  a  layer  nf  slroiij.' 
clastic  tissue,  and  this  expands  to  a  K'i"'-ater  <n'  less  iU-irvrv  at  each 
heart  beat.     The  resistance  wliich  the  arteries  and  th.   .'apillaries 


AKTKItlAI,    Hl.lMiIi    I'lil'.SSlUi:. 


173 


ofTf?'  to  till'  How  of  blood  prevents  the  pnssiijje  of  tlie  entire  sys- 
tolic output  of  tile  heart  into  the  veins  dui-iiiff  the  acluiil  ven- 
tr'ieiilai"  eonti'aetion.  It  is,  thei-efore.  neeessai'v  that  the  lai'tre 
artei-ies  expand  in  order  to  make  i-ooni  for  the  hlood.  A  part  of 
the  enerfjy  of  liie  heart  heat  is  stored  up  in  the  elastic  coats  of 
the  arteries,  and  after  closure  of  the  semilunar  valves,  which 
^iiard  the  ventricular  orifice,  the  hlood  in  the  distended  arteries 
is  forced  on  throut;h  the  capillaries  by  the  pressure  of  the  ar- 
terial walls. 

Arterial  Blood  Pressnre.-Fnni I  the  loreffoinsr  description  we 
see  that  tliric  are  severai   factor's  which  contribute  to  the  niain- 


Vi'r^  -*t  l>i;i«r.mi  "!'  '-xp*  rim»'Tit  lo  stinw  how  ;i  iiiilsi-  i  |ii'imIii<-<-i1  lt\  i-uin- 
IiicKsiti*;  '111-  hiilli  /■' I  .(iiiiHS  til  ll-^iiiiiii'iir  vvlnii  lluid  lliiws  thrniiKli  mi  liMstn 
mill'  I /•' 1  wliiii  thiTi-  IS  ii'sist  .  '  !■  1(1)  '■  ihi'  iiiilflow.  .1,  linslii  of  wiit.'f  ; 
11.  Inilli  s\  i-iiiiii- :  ''  :m<l  f  .  ■"■•p  iiicks  li  iuiil  tulii';  /•'.  rlnslir  tiilu' ;  I!, 
liulli    lilli"!    with    Hiiiiiii:'- 


teiianc  i)f  a  constant  si  ream  of  nlood  through  tlu'  capillaries: 
vi/..  tlv-  |>unipin<r  aciioii  of  the  lu-art.  the  resistance  (»f  the  ar- 
terioles and  capillaries,  tl'e  elastic  recoil  of  the  blood  vessels,  and 
the  ani.*unt  of  bl»MKl  itself.  That  the  velocity  and  the  jiressure 
ai'  tlie  blood  dejH'nd  (Mi  1hes«-  factors  was  first  of  all  demonstratetl 
ii-'  17:!'J  by  |{ev.  Steplien  Hales,  who  in  a  book  published  in  that 
yeai  reports  havinjr  experinieiiialiv  .h  ierinineil  the  blood  pres- 
sure Mt  the  femoral  artery  of  a  horse,  ile  found  that  the  pres- 
sure was  sutTiejeiit  to  raise  the  bliMnl  in  a  tubi-  siven  feet  above 
the  level  of  the  heari.  au<i  be  ali«>  observed  that  each  In-at  of  the 
heart  and  each  res|nratur\  movement  affected  the  pressure  of  the 
blood.  The  |)ressure  exerti'd  b\  the  blood  on  the  vessel  wall  at 
the  heiffht  iif  the  systole  of  the  vent  rich  is  knou  n  as  the  siislvlii- 
hhitiil  pnssitn.  and  that  exerted  by  ilie  elastic  ncoil  of  the 
arterb'S  on  the  blooil  during  the  diastole  of  tin    heart  is  known 


174 


IMIYSIOI,(MiY    K<l|{    DKNTAIi 


TI'DRNTS. 


'ij 


as  the  (lia.sfoli,    binoij  pnssiin.     The  avcrjij.'.'  Ix-twocii  tli.-sp  two 
piVHsums  is  c'all<Ml  tli<'  avfi-iitf.'  or  ni.^iiii  iirtn-iiil  hlood  j)rf.s.siin'. 
Since  Hale's  experiment  bett.T  ajiparaHis  has  he.-n  devised  to 


KiK.   I'l.— Apparatus  for  lakiiiK  a  trai-ing  of  the  h    . ,.;  ,.,,.s.sur.. 

measure  the  l.lood  pressure  in  animals  under  different  eonditions. 
The  standard  metluxi  eoiisists  in  idaeing  a  tube,  ealled  a  eannula. 
direetly  into  a  hlootl  v.'ssel.  This  is  eonneeted  with  a  rulil^.r 
tid)e  tilled  with  an  anti-elotting  mixture  (see  Fijr.  31  i  with  one 
arm  of  a  I'  tube  partly  tilled  with  niereury.  Wliei-  the  bloofl  ves- 
sel is  (.pened.  the  pressure  of  tiie  blwxl  will  force  the  mercurv 


ARTEKIAt,    m-<MtH    I'HKSsrUf'.. 


175 


down  ill  0111'  arm  and  up  in  the  otlwr  arm  of  llic  V  liihc.  Tlif 
(liffi-rt'iicv  hi'twcfii  tlip  levels  of  the  mcn-iiry  in  tlic  two  arms  miil- 
tiplit'd  by  ]:\.'i,  the  specifi^c  gravity  of  inereury.  nives  the  jnes- 
Hure  of  the  l)loo<!  in  terms  of  water,  or.  as  is  usually  doni'.  the 
hlood  j)i-essiire  is  expressed  as  the  number  of  miiliiiielres  tliroii^h 
whieli  the  inereury  has  been  raised. 

Determinations  of  the  pressure  existinj:  in  ditVereiit  portions 
of  the  vascular  system  show  that  tliere  is  a  steady  decrease  of 
jiressure  of  the  blood  from  the  aorta  to  the  entrance  of  the  vena 
cava  into  the  ri}?ht  auricle.  Jt  thus  hai)peiis  that  tlie  blood  is  al- 
ways tlowinp  from  a  place  of  hiiirher  pressure  to  one  of  lower 
pressure. 

Methods  whicli  are  of  much  jtraetical  importance  in  the  diai;- 
iiosis  of  vascular  diseas«'s  have  been  th'vised  to  determine  the 
blocMl  pressure  in  man.  The  principle  of  these  methods  consists 
in  measiirin'T  the  i)ressure  rei|uired  to  shut  oil*  completely  ttie 
blood  sui)ply  in  an  artery.  This  is  accomplished  by  placiiifr  a 
rubber  sac  encased  in  a  leather  band  about  tiie  arm.  ( Ki«.  22). 
I'ly  means  of  tiibinfi  this  sac  is  connected  with  a  mercury  ^i'tijre 
and  an  uir  pump.  When  the  sac  is  luimped  np  with  air,  the  ves- 
sels in  the  arm  are  pomi)ressed,  and  wiien  the  blood  can  no  longer 
force  its  way  under  the  obstruetio'i.  the  pulse  at  tlie  wrist  disap- 
pears and  at  this  moment  the  height  of  tlie  men-nry  in  the  jjaufre 
is  measured.  This  represents  the  systolic  blood  pressure.  If  de- 
sired, a  similar  measurement  mav  be  made  in  thi'  arteries  of  tin- 


To  niiasiire  the  dia.stolic  pressure  is  moit-  diftienlt.  The  method 
depends  on  the  exjM'rimeiitally  determiiieii  fact  that  when  the 
pulse  wa  prt«lueed  in  tlie  artt-ri-*  l»>  each  systole  of  the  heart, 
is  of  greatest  amplitu  ir.  th.  pf.-s<«n-  in  the  air  sac  or  compress 
inj^  band  etpials  the  lowest  pieSMU  '  present  in  the  vessel  hi  IWeell 
the  pulses. 

Recently  improvements  have  Iteeii  .iiade  in  the  ii.etho«l  of  jiulir- 
mg  ihe  point  uf  obliterittion  of  lh«  i.rtery.  and  also  the  \h^uX  of 
tmixitinnn  |iu!sation.  by  lislentJig  to  the  sounds  prcvjuced  at  ea -ii 
ftnt^xk    WHM'  wh-n  tl:e  arttrv  i>  iM'ing  eoTii|H-i-s.sed 

■fV  systolic  blood  pressure  iu  the  artery  ol  the  arm  in  health v 


jm^mE^KI* 


17(J 


l'IIV,«.|(i|,(HiV    Kitlt    KKNTM,    STIDIATS. 


youiifr  men  vai-i.s  from  110  to  l:i()  mm.  oi  m.ivury  wlicn  it  is 
ilclcrmiiicd  in  tiir  sittiii^r  postiiiT.  When  ii  p.-rsnii  is  lyinij  down 
the  |ii-fssniv  is  ii  little  less,  iind  after  hard  exi-rcise  a  little  hi-jher. 
The  blood  pressure  under  ordinary  conditions  i-  relatively  con- 
stant, and  is  dependent  on  a  delicati-  adjustment  !•  tl.e  relation- 
ship existinjr  between  the  force  of  the  heart,  the  amount  of  bUxtd 


Vin.    22. — .\|i|iai;itiis    fni     iniii.^uriim    tin-    :irli  ii:i;    I.I i    jncsKurc    in    w.ni. 

Thi-  |if.-sHUi'.  in  111.  .ufi  is  i-ai..^iil  i.y  in.  ,iiis  ..I'  il.>  syiinK.'  until  III.'  piilsi- 
..in  II..  Iiiiin.i  I..-  r.  It  at  thf  wrist  Tliis  iii-rss..i.  .  r.a.l  ..IT  .111  tli,.  m.-i.-my 
iii;iiiiiiii.-I.'i     .s>.^t..(if   pfcssur.- 1. 


liumjMMl  at  ea.-h  Ixiit.  the  resi.stane.  which  the  walls  of  the  blood 
vessels  olfer  to  the  tlow  (d'  till-  iiiiiod.  the  si/e  of  f|ie  vascular  svs- 
teiii.  and  the  aiiioiinl  of  IiIimmI  in  tin  body.  Since  tin-  am. -nut  of 
blood  in  the  boily  i«  relatively  coiistaiif.  we  may  >,!i\  ilial  the 
factors  which  cjiaiii;e  aiv  the  heart  and  the  blood  vc^w-ls.     How 


T!iK  VKi.itriTY  OF  TiiK  nrxM»n 


177 


llii'sc  fiH'liii's  iiiHiii'iii'f  till'  liloitil  |>i'fssun'  may  lie  sci'ii  if  we  iij,'aiii 
conipiii"  till'  system  to  tli'  city  wati-r  supply. 

Factors  Which  Maintain  Blood  Pressure. -Wii.n  the  most 
Wiitci-  is  ht'iiifr  piimpi'd  into  the  mains,  tlifii  tlit'  water  has  tlie 
jjn'iitest  velocity  and  pressure.  Likewise,  when  the  heart  is 
puinpinfj  most  Idotwl  into  the  aorta,  the  vel  )eity  ami  the  pressure 
of  hlood  in  the  vessels  are  the  jrreatest.  If  the  amount  of  water 
remains  constant,  a  uniform  outflow  throuj^h  all  the  outlet  tubes 
will  he  maintained,  hut  if  the  number  of  outlet  tubes  be  diiuin- 
ished.  then  more  water  will  have  to  How.  |>  r  minute  of  time, 
throuffh  the  renuiininu'  tubes;  hem-e  the  velocity  and  the  pres- 
sure must  be  increased. 

The  .same  conditions  are  present  in  the  bcxly.  A  narrowing  of 
the  arterioles  throu},diout  the  Imdy  or  in  some  e.vteiisive  vascular 
area,  causes  the  pressure  and  the  \.'locity  of  the  bl(K>d  to  be  in- 
creased in  the  remaining;  vessels,  provided,  of  course,  the  heart 
beat  is  unclianjjed.  A  dilation  of  the  arterioles,  on  the  other 
hand,  results  in  a  fall  of  j)ressurc  and  a  decrca.se  in  the  velocity 
of  the  .bl(M)d.  In  the  same  way  also  an  increase  or  decrease  in  the 
action  gf  the  heart  will  result  in  an  increase  or  decreas*-  in  the 
l»ressure  and  velocity  of  the  bloml. 

The  dei)cndciice  of  flie.se  two  factors,  i.  c,  the  !  rt  and  th» 
vascular  system,  on  the  mainteii'incc  of  the  normal  blood  pres 
sure,  is  .seen  in  the  fact  that,  with  a  fa.st  heart  and  dilated  blooii 
vessels,  the  blood  |»res,sure  may  be  exaetlv  the  same  as  when  th.- 
heart  is  beatiufr  very  slowly  l)ut  the  arterioles  are  all  c(mstricted. 
It  is  apparent,  therefore,  that  the  velocity  of  the  l)lood  in  the 
ves.sels  is  dependent  du  the  pressure  of  the  blood  and  the  extent 
of  the  viiscular  area  at  the  time  in  (|Ucstion. 

The  Velocity  of  the  Blood.— Hy  the  velocity  of  the  flow  of 
blood  we  mean  the  actual  time  it  takes  for  a  particle  of  blood  to 
jtass  between  two  points.  If  the  rate  were  uniform  throughout 
the  vascular  area,  we  could  compute  the  time  which  a  particle  of 
blood  would  take  to  j)ass  through  the  circulatory  system.  This 
is  not  the  ca.se,  however,  for  tlu-  flow  of  blood  is  much  swifter  in 
the  aorta  than  in  the  snudler  vessels,  and  here  again  our  analogy 
between  the  circulatory  system  imd  the  city  water  system  applies. 


178 


rHVsl(ll,(H;V    Fi)H    hlATAI,    STIIHATS. 


I    .    s 


Just  as  tlic  coniliiiKMl  cmss  area  of  the  small  pipes  Icadirif,'  from 
flic  main  pipe  of  the  water  svstem  is  greater  l»y  many  times  than 
tlie  area  of  the  main  jiipe.  so  it  hits  been  estimated  that  the  total 
cidss  section  of  the  eajiilinries  of  the  IxmI.v  is  HUO  times  lar>rer 
than  that  of  the  a.irta. 

It  has  been  estimated  that  the  rate  of  l)l(M)d  flow  in  the  aorta  is 
about  ;{20  nnu.  ju-r  second.  The  aveui^  •  rate  of  flow  in  the  capil- 
laries must  then  be  f<()0  times  less  than  that  in  the  a(»rta,  or  0.4 
nun.  per  second.  As  the  lenytli  of  a  capillary  has  been  estimated 
to  Im'  about  0.r»  trim.,  the  blood  takes  about  a  sicond  to  j»ass 
through  them  into  the  veins.  This  has  been  verified  by  mici'o- 
.scopic  txiiiiiination  of  the  bhxxl  flow  in  the  capillaries. 

The  velocity  of  the  Mood  must  be  altered  whenever  the  size  of 
th 


e.\ 


le  viisi'  liar  area  is  (  linnncd.  and  since  during!:  a  cardiac  cycle 
iicfl.\    till-  same  .iino'aiit   of  blood   is  delivcj-ed   into  the  ri|^ht 


auricle  as  the  left  ventricle  forces  out  into  the  aorta,  it  follows 
that  the  same  amount  must  pass  thron^di  the  vascular  area  of  the 
body  in  the  .same  time.  In  other  words,  the  amount  of  blood 
which  flows  in  a  jfiven  series  of  blood  vessels  in  a  <riven  time  is  in- 
depenilcnt  of  the  size  of  the  blood  ves.sels. 

The  Return  of  the  Blood  to  the  Heart.  -We  must  now  i- 

sidcr  the  nature  of  tlu  force  which  j)roj)els  the  blood,  and  study 
what  chanjres  take  place  in  the  movi'iiient  of  the  blood  duriiitf  its 
})assajre  throuKh  the  vessels. 

The  blood  is  expelled  from  the  left  ventricle  with  consi.lcr- 
able  force  an<i  at  a  hi^rh  v,i..-i!y.  On  its  way  throufjh  the  body 
much  of  the  eiicrfry  jri\  ii  >  lit  by  the  contraction  of  the  heart  is 
used  to  overcome  th;-  rr,i.stance  offered  by  the  walls  of  the  ves- 
.sels and  the  capillaries.  In  coiLseipieiice  of  this,  the  velocity  and 
the  ])ressure  of  the  blood  on  Mie  sides  of  the  vessels  are  much  i-e- 
ilnced. 

The  blood  is  collected  fidin  the  capillaries  by  the  veins,  and 
since  the  volume  of  the  veins  is  l.-ss  than  the  volume  of  tin  cai)il- 
laries  its  velocity  i,-;  mueh  iiicrea.sed.  The  relatively  lai'jje  calibre 
of  the  veins,  however,  ort'.-rs  little  resistance  to  the  flow  of  blood 
and  the  eiieixv  rcmainintr  from  that  imparted  to  the  blood  by  the  . 
heart  has  full  power  to  niake  it.self  felt.    Nevertheless,  this  is  not 


TiiK  ("iRrrr.ATioN  tim;;.  179 

sufficient  alone  to  foree  tlie  Itlooil  onward  an. I  liael;  to  tlie  lieart. 
Hn<l  we  must  seeix  oflnr  imissurii  fiKlors  to  i.ii>liiin  llu  i-(  nous 
n  liini. 

Tlie  veins  are  eiiuiiiped  with  eup-sha|>e<l  valves  wliieli  permit 
the  passnjre  of  I>Io(kI  only  in  one  direction,  i.  e,,  towards  the  heart. 
Kvery  movement  of  a  muscle  therefore  si|neezes  some  of  the  lihwid 
onward.  This  massajfinjf  influence  of  the  m'lscles  is  very  im- 
portant.    Its  absence  accounts  for  the  fact  that  it  is  impossdile 

to  stand  .still  for  a  lonn  jM'riod  of  time  without  th.'  Iind>s  1 m- 

\i\g  very  painful,  especially  in  the  case  of  varicose  veins,  where 
the  valvcH  of  the  veins  are  no  longer  functional,  .so  tliat  there  is 
nothing  to  prevent  the  blood  from  returning  to  th"  more  <lepeiid- 
ent  positions.  Another  source  of  energy  to  the  returning  bli>iid 
is  the  aspiratory  ctFect  of  the  thorax  at  each  inspiration.  This 
action  will  be  considered  in  the  study  of  the  i-espiratory  mech.in- 
ism. 

Circulation  Time. — The  actual  time  which  is  taken  f<ir  the 
bloiMl  to  traverse  tlie  circulatory  system  has  been  variously  esti- 
mated. Obviously  such  figures  can  give  only  average  results, 
sini-e  the  distance  through  wliicli  blood  to  the  arm  must  flow  is 
less  than  that  to  the  legs.  In  general,  it  may  be  siiid  that  the 
blood  makes  a  complete  circulation  in  from  2.")  to  :!()  lieats  of  the 
heart.  The  circulation  through  the  lungs  re«|uire^  about  one- 
fourth  of  this  time. 

That  the  velocity  of  the  blood  flow  through  litfereiit  ves,sels 
varies,  is  apparent  from  actual  observations  made  on  severing 
them  and  actually  observing  the  rate  of  outflow.  The  following 
figures  expressing  the  hloitd  s\ipi>Ui  i>ir  uiiinih  li,  lach  hinidrnl 
firamuus  of  ornmi  have  been  (b'tcrmined  experimentally: 

lj,.g    .")  c.  c.  Liver    (venous)....    ")!>  c.  c. 

Head    20    "  Liver    (arterial )  .  .  .   'i'y 

Stomach 21     "  I'.rain    \'-M> 

Intestines  ...  .;n     "  Kidney  l-'iO 

Spleen    -"iS    "'  Thyroid    MH)    " 

The  Effect  of  the  Circulation  on  the  Blood.— If  llu-  <irciila- 
tion  of  the  blood  through  the  ves.scls  of  the  lung  or  the  web  of  a 


MICROCOPY  RESOLUTION  TEST  CHART 

NATIONAL  BUREAU  OF  STANDARDS 

STANDARD  REFERENCE  MATERIAL  1010a 

(ANSI  and  ISO  TEST  CHART  No.  2) 


II 


Si 
f 

It  •'  ■ 


i  i-t 


180 


PHYSIOLOGY   FOR   DENTAL   STUDENTS. 


frog's  foot  be  pxamined  by  moans  of  a  niicroseope,  several  inter- 
esting faet«  will  be  noted.  The  I'ed  blood  eorpuseles  will  be  seen 
flowing  in  tlie  center  of  the  blood  ves.sels,  while  in  the  elear  plan- 
ma  which  surronnds  them  are  the  much  less  numerou'^  white 
cells.  This  arrangement  is  explained  by  the  fact  that  the  red 
corpuscles  are  heavier  than  the  white  cells  or  the  plasma  and  are 
held  in  the  center  of  the  stream  by  a  principle  of  hydraulics.  The 
white  cells  flow  more  slowly  along  the  sides  of  the  vessels  than 
the  red  corpuscles  do  in  the  center  of  the  stream,  which  is  sug- 
gestive of  the  function  of  the  white  cells  as  phagocytes  (see  p. 
152)  ;  thus,  any  injury  to  the  ves.sel  wuU  will  necessarily  slow  the 
flow  of  blood  through  the  veins  and  allow  a  greater  number  of 
leucocytes  to  collect  at  the  point  of  injury. 

The  Pulsatile  Acceleration  of  Blood  Plow.-  The  flow  of  blood 
in  the  arteries  differs  from  that  in  the  veins  and  the  capillaries 
in  that  it  is  swifter  and  pulsatile  in  character.  This  pulsatile 
variation  is  due  to  the  acceleration  of  the  bloo<l  flow  caused  by 
each  heart  beat,  and  the  reason  that  this  is  not  .seen  in  the  capil- 
laries and  veins  is  that  the  resistance  which  the  walls  of  the 
capillaries  and  arterioles  offer  to  the  bloo<l  is  so  great  that  the 
cardiac  factor,  acting  only  for  a  brief  time,  is  lost.  The  energy 
represented  in  the  increase!  rate  of  flow,  is  spent  in  stretching  the 
walls  of  the  arteries,  which  contract  after  the  pulsatile  wave  has 
passed,  and  thus  force  the  blood  onward. 

The  Pulse. — The  pulsatile  expansion  of  the  arteries  at  each 
heart  beat  has  b<'en  mentioned  in  connection  witli  the  factors 
which  help  to  maintain  the  normal  blood  pressure.  It  is  this 
also  which  pro<luces  the  phenomenon  which  is  known  as  tlie  pulse. 
From  time  immemorial  the  physician  has  been  accustomed  to 
come  to  an  idea  concerning  the  condition  of  the  circulation  by 
feeling  the  pulse,  for  it  represents  changes  in  the  arterial  ten- 
sion occurring  dui-ing  each  cardiac  cycle.  In  order  to  study 
tlie  pulse  wave  more  carefully,  instruments  have  been  devised 
which  graphically  record  its  wave  on  a  [liece  of  paper.  Such  an 
instrument  is  known  as  a  sphifymoffroph  {Fig.  2:3),  and  some 
of  these  have  been  cleverly  arranged  so  as  to  enable  us  to  record 
simultaneously  the  pulse  from  different  blood  vessels. 


THE  PULSE. 


181 


Since  the  pulse  is  not  due  to  an  aetuiil  niovt'inciit  of  Mood 
along  the  arteries,  ])ut  ratlier  to  elianges  in  tension  producing 
an  expansion  of  the  vessel  wall,  it  follows  that  tlie  transmission 
of  the  wave  may  be  much  more  rapid  than  the  movement  of 
l)loo<l.  This  may  be  explained  by  reference  to  the  motion  im- 
jiarted  to  a  row  of  billiard  balls  when  the  one  on  the  end  is  hit 
with  the  cue.  The  one  hit  a'  tually  moves  very  little,  but  imparts 
its  energy  of  movement  to  the  othei-s,  so  that  tlie  ball  at  the  end 
of  the  row  moves  away  with  some  velocity,  while  tlie  others  move 
slowly.     The  wave  of  energy  sjireads  in  a  fraction  of  a  second 


KiR.   23. — Jaquet  SphyKiiiocardioKiaph. 


from  ball  to  ball.  l?y  simultaneously  taking  tracings  of  tiie  caro- 
tid and  the  radial  pulses,  foi-  example,  it  has  been  computed  that 
the  pulse  wave  is  transmitted  at  the  rate  of  ten  metres  a  second, 
and  that  it  may  be  six  metres  long.  This  means  that  the  pulse 
wave  reaches  tlie  periplu^ral  vessels  before  the  systole  of  tiie 
heart  is  complet"d.  Any  local  change  in  tlie  vessel  may  slow 
down  the  rate  of  transmission,  and  if  there  is  a  difference  in  the 
appearance  of  the  pulse  in  the  two  arms  or  legs,  it  is  indieativi> 
of  some  obstruction  or  change  in  one  of  the  vessels. 

When  wo  analyze  the  pulse  wave  obtained  by  a  spliymograph 
taken,  for  example,  from  the  radial  artery,  it  is  seen  that  the 


182 


PIIYSI0L(10Y   FOB   DENTAL   STUDENTS. 


<Mst  elevation  is  very  rapid  and  abrupt  (Fig.  24,  a).  This  is 
aused  by  tlie  sudden  inerea.se  in  pre-ssure  of  tlie  blood,  due  to 
eardiae  systole.  resultin«f  in  the  sudden  e.\pansion  of  the  artery. 
Following  the  abrupt  rise,  the  eurve  gradually  descends  till  the 
ne.\t  heart  beat  oeeurs.  During  this  i)eriod  the  arterial  blooil 
l)ressure  is  maintained  by  the  elastic  recoil  of  the  stretched 
arteries.  On  tlie  descending  eurve  there  are  as  a  rule  several  small 
waves  and  depressions.  Of  these  waves  the  large  one  (Fig. 
24.  b)  is  always  present  and  is  known  as  the  dicrotic  wave,  and 
the  dicrotic  notch  is  tiie  de[)re.ssioii  immediately  preceding  the 
wave.  The  i)resence  of  this  wave  is  explained  as  follows:  At 
the  end  of  cardiac  systole  the  blood,  under  the  influence  of  the 
pressure  exerted  by  the  stretched  walls  of  the  arteries,  is  forced 
both  towards  the  perijiheral  vesisels  and  back  towards  the  heart. 


KIg.    24. — Pulse   tracing  made   by   sphygmograph. 
(liciotic  wave. 


A.    systolic    wave 


;i!: 


i 


if  ;■ 


Itii! 


The  cardiac  semilunar  valves,  being  tightly  closed  at  the  end 
of  systole,  arrest  the  back  flowing  blood,  and  it  rebounds,  as  it 
were,  jiroducing  the  de])res.sion  with  the  wave  (a)  which  is  re- 
flected over  the  entire  circulation.  When  the  blood  pressure  is 
high,  the  .secondary  waves  make  very  little  depression,  because  of 
their  relatively  low  pressure,  but  in  conditions  where  the  blood 
l)res.sure  is  low,  as  in  typhoid  fever,  .surgical  shcek.  a  faint,  and 
in  deep  anesthesia,  the  dicrotic  wave  is  easily  felt  by  the  linger. 
Other  (|ualities  of  the  pul.se  which  may  assi.st  the  phy.sician  in 
.judging  of  the  condition  of  the  circulatory  system  are  its  rate, 
and  its  compressibility.  Its  rate  tells  us  how  fast  the  heart  is 
beating,  and  its  compressibility  gives  a  rough  idea  of  the  blood 
pressure. 

The  Circulation  Through  the  Lungs.— In   general   the   same 
conditions  are  present  in  the  circulation  of  the  blood  through 


TllK    ITI.MONAKV    CIKCir.ATION. 


183 


tin-  luiifis  as  arc  fouiul  in  tlic  systfinic  circulation.  Tiic  ritrht 
ventricle  is  far  less  i»o\verfiil  than  tlie  left,  so  tliat  tiie  pressure 
of  tile  blood  in  the  limn  vessels  is  less  than  that  in  the  systemic 
vessels.  The  respiratory  movements  also  cause  the  si/.e  of  the 
blootl  ves.scls  in  the  lunjis  to  vary  in  a  marked  degrei'.  These 
changes  in  the  capacity  of  the  pulmonary  hloml  vessels  atTect  the 
sy.stcmic  blood  pres.sure.  Tims,  at  the  iicittht  of  inspiration,  the 
liiDKS  may  contain  one-twelftii  of  the  blood  of  the  body,  while 
during  expiration  this  amount  may  be  lessened  to  one-fifteenth 
to  one-ei<rhteenth  of  the  total.  This  condition  makes  it  possible 
for  the  heart  to  be  tilled  more  rai)idly  during  the  later  i)art  of 
inspiration  and  tlw  beginidng  of  expiration,  than  at  other  times, 
and  accounts  for  the  rise  of  blood  pressure  observed  at  this  time. 


h\ 


("HAl'TEK  XX. 

TIIK  riRC['LATION  (Cont'd). 

The  Influence  of  the  Nervous  System  on  the  Circulation. 

I'V  to  the  presfut  time  we  have  coiisidcivd   tlu-  ciroiilatory 
system  as  a  purdy  automatic  and   mwhanieal   apparatus   foV 
carrying  of  blood  to  all  parts  of  th."  body.    It  is  i.(.e(.s,sary  that 
tins  apparatus  vary  in  its  activity,  not  onlv  according  to  tb.- 
ncwls  of  the  body  as  a  whole,  but  also  according  t..  ^he  needs  of 
the  various  parts  of  the  bo<ly.    It  would  be  poor  economv  for  th«> 
heart  to  maintain  thrcugh  all  parts  of  the  botlv  at  all  times  a 
.stream  of  blood  which  would  be  large  enough  for  all  emergenci.-s 
There  must  be  sonje  way  of  controlling  the  blood  flow  accordin- 
to  the  needs  of  the  body.     This  function  is  served  primarily  by 
the  central  nervous  sy.stem.  which    is   connected    bv    means   of 
i.erves  with  the  musculature  of  the  heart  and  the  bloo,l  ve.s.sels. 
an.l  .secondarily  by  .secretions  from  the  .so-called  ductless  gbmds 
th.-  best  known  of  which  are  the  adrenal  glands  (see  p.  12!)). 

The  Nervous  Control  of  the  Heart. 

The  Cardiac  Nerves.-The  heart  is  supplied  with  b„th  s.-n- 
sory  and  motor  nerves.  Sensory  nerves  carrv  stimuli  from  th.' 
per.i)he-a)  regions  to  the  brain  and  are  known  as  afferent  nerves 
Motor  nerves,  on  the  other  hand,  carry  stimuli  from  the  brain 
to  the  mu.scles  or  glands,  and  are  known  as  efferent  nerves  The 
efferent  nerves  of  the  heart  are  found  in  fib-rs  coming  from  the 
s|)inal  cord  by  way  of  the  .sympathetic  .sy.st.-.n,  and  bv  tiu-  vagi 
or  the  tenth  pair  of  cranial  nerves  (.see  p.  26.'.).  It  m.i.st  be 
clearly  understood  that  the  nerves  merely  regulate  th.-  h.-art 
beat,  but  have  nothing  to  do  with  its  occurrence.  In  other  words 
the  heart  continues  to  beat  aft.-r  nil  the  nerv-s  hav.-  b.vn  .s..vere<l' 

The  Accelerator  Nerves.— To   understand    h..w   the   »ib,.rs 
reach  the  heart,  the  reader  is  referred  to  the  general  description 

184 


THE  CARDIAC  NKKVES. 


185 


of  the  .syiiii)atlit'ti('  lUTVous  systi'in  on  panf  277.  Tlic  synipatlictic 
fibers  of  the  heart  arc  fouiitl  in  the  first  and  st'cond  spinal  nerves 
of  tlie  tlioraeie  region.  After  eonneeting  with  nerve  eells  sitn- 
at<'(l  in  tile  stellate  ganglion,  they  go  to  the  heart,  where  they 
end  about  the  eardiae  nniseular  fibers. 

Cutting  the  synipathetie  fibers  to  the  heai1  eau.ses  a  .slower  beat 
and  a  prolonged  diastole.  On  the  other  hand,  stinndafion  of  the 
nerves  with  an  eleetrie  eurrent  increases  the  rate  of  the  heart 
(Fig.  2.')).  For  the  above  reasons  the  synipathetie  nerves  to  the 
heart  are  known  as  (icidtriitor  or  <iii(/>H(  iilorij  nerves. 

The  Inhibitory  Nerves. — The  vagi  are  a  pair  of  nerves  arising 
on  eaeli  side  of  the  medulla,  and  running  a  eourse  downwards 
through  the  neck  into  the  thoraeie  and  abdominal  eavities.  This 
pair  of  nerves  sui)ply  fibers  to  the  various  organs  of  these  regions 


Time  in  icconds 


FiK.  2.1. — Kffect  i>f  stimuliitiiiK  vaKUs  and  s.viniiuthi'lk-  luTvcs  lui  tln'  fn 
hi'Uit. 


ineluding  the  heart,  whieb  receives  branches  from  both  vagi. 
It  is  passible  l»y  simple  exporiiiiouts  to  demon.strate  the  function 
of  these  fibers. 

For  example,  if  the  vagus  on  one  side  be  cut.  the  heart  rate 
will  increase  a  little;  if  both  vagi  be  cut,  the  beat  is  still 
more  markedly  (luiekened.  and  the  increased  discharge  of  blood 
from  the  heart  produces  a  rise  in  the  arterial  blood  pressure 
(Fig.  26,  No.  Ill  ).  By  cutting  these  nerves  we  remove  the  infiu- 
•;ice  which  the  central  nervous  system  exerts  through  them  on 
the  heart  rate.  Since  flu  heart  beats  faster  after  this  operation, 
we  nui.st  conclude  that  this  organ  constantly  receives  stimuli 
from  the  brain  through  the  vagi,  and  that  these  stimuli  cause 


-  }■' 
■  f- 


♦ 


186 


Kldn«y  Vplmm 


PIIYSIOMKIY   FOR   DENTAL   STl'DENTS. 

y 


/>/vA' 


Kidrny  Volumt 


•  Stimulatien 
aplenchnic 


Tlnn  m  Mcond) 


No.I 


No.n 


_Kldr)«y  Voiu">c 


idity  v/olume 


Blood  pr*>}ur«  ^    ^  .  . 


>«rv«  Cut 


Muod  pressure 

*  Iniccfcion 
of  dilute 
odrcnolin 
solution. 


Tin*  in  Mconds 


Tinie  In  seconds 


no.ni 


No.EZ' 


Kidney  Volvme 


Rapid   bleedinj    'Alow  bleedins 


Time  in  seconds 


No.Y 


FlK.  26. — Tradiiss  of  arterial  hluud  pressuiv   (taken  with  apiiaratu.s  in  Fis- 
21)  and  of  Itidney  voluiHf  (tal<en  with  volume  recorder)  showing  the  effcet  of; 
T.      Stimulation  of  the  vaKua   nerve. 
II.     Stimulation   of  the  .splanchnic   nerve. 

III.  Cutting  one  vaKua  nerve. 

IV.  Injection  of  epiiiephrin   (adrenalin). 
V.      Hiemorrhage. 

The  tracings  all  read  fruMi  riyht  to  lift. 


THE    CARDIAC    NERVES. 


187 


tin-  heart  to  boat  mor»'  slowly.    Such  a  poiitimu'd  action  of  a  nerve 
\h  known  as  a  tonic  influence. 

That  the  va^i  can  slow  the  heai-t  or  even  stop  it  altogether  is 
shown  by  stimulation  of  tiiese  nei-ves  with  an  electric  current  of 
suitable  .strength  (Fig.  2")).  If  weak  shocks  are  eniploycl,  the 
heart  is  slowed,  the  bl()o<l  iiressuiv  falls  somewhat.  an<l  the 
iliastolic  pres.sure  becomes  markedly  decreas«'d,  because  tlie  ar- 
teries have  a  greater  jjcriod  of  time  in  which  to  empty  Ih-tween 
the  b*'ats.  If  somewhat  stronger  stimuli  be  used,  the  heart  will 
stop  beating  entirely,  and  remain  in  the  iliastolic  position  for 
sevc  1  s! '-onds,  during  which  the  blood  pressure  will  sink  to 
z.    .  16.  No.  1).     It  is  scarcely  possible  to  kill  an  animal 

,'  •li'-n  of  the  vagus,  however,  since  the  heart  will  In'gin 

1      ..  .     a  short  time  in  spite  of  the  continued  vagus  stimu- 

lal.o...  '"hiis  phenomenon  is  known  as  escapemoit.  The  time  of 
its  onset  varies  considerably  in  different  animals.  It  has  been 
suggested  that  the  vagi  have  much  more  effect  on  the  auricles 
than  on  the  ventricles,  which  is  suggestive  of  the  auricles  In-ing 
the  pacemakers  of  the  heart. 

Relation  of  the  Sympathetic  and  Vagiu  Nerves  to  the  Heart. 
— Tile  antagonistic  action  existing  between  tiie  cardiac  fibers  of 
the  8ymi)athetic  and  vagus  nerves  allows  the  heart  to  respond 
([uickly  to  any  need  that  the  body  may  denuind  of  it.  These 
demands  are  made  through  the  brain,  by  various  afferent  or  sen- 
sory nerves.    This  is  brought  about  in  the  following  wa.y : 

The  Cardiac  Centre. — In  the  medulla,  tiie  hind  part  of  the 
brain,  there  is  a  collection  of  nerve  cells  from  which  the  cardiac 
branches  of  the  vagus  arise.  Near  by  also  are  located  the  cells 
from  which  the  sympathetic  nerves  of  the  heart  arise.  Hoth  of 
these  nerve  centers,  for  by  this  term  are  known  the  important 
cell  stations  of  the  brain,  are  supplied  by  extensive  connections 
with  afferent  or  sensory  fibers  coming  from  all  parts  of  the  botiy, 
the  brain  and  even  the  heart.  The  centers  become  more  (  ■  less 
active  in  response  to  im|)ulses  reaching  them  along  the  sensory 
fibers. 

The  Cardiac  Depressor  Nerves. — One  of  the  most  important 
of  the  different  cardiac  nerves  is  that  known  as  the  cardiac  dcpns- 


188 


•IIYSIOlAKJY   F,)H   DENTAti   STPDENTS. 


\i  K- 


sor.   It  has  its  Ih'jfiiuiiiijrs  in  filnnnMits  iyinjr  in  the  l.-ft  vc-ntricl.' 
HM(1  in  th«'  aorta,  and  nins  to  the  nii-diilia  in  the  vaRiis  trunk,  in 
most  nunnnials,  or  as  a  separate  n.-rvc  i.i  ti„-  rabbit.    I'nd.r  ordi- 
nary conditions,  cuttintr  tliis  nt-rvi-  prmlu'-es  no  .'fffcf    on  the 
heart  Ih-at,  but  stinmlation  of  the  upper  end  (»f  the  cut  nerve, 
i.  e.,  the  end  running  to  the  head,  residts  in  a  marked  slowing  of 
the  heart  and  fall  in  the  blood  i)re88ure.     If  the  experiment  is 
repeated  after  eutting  the  vagi,  the  heart  is  slowt'd,  but  the  fall 
in  blood  pres.siire.  though  le.ss  evident,  still  oeeurs.    The  normal 
stimulus  to  tlie  depressor  nerve  is  a  high  blood  pressure  in  tlie 
ventrieles  and  aorta.    Tlie  stimulus,  thus  s«"t  nj),  aets  throutrh  the 
vagus  eenter  and  the  vagus  nerve,  and  slows  the  heart.     It  also 
aets   on    the    vasomotor    eenter  and  causes  the  blood  vessels  to 
•lilate.    Hoth  changes  produce  a  fall  '.n  the  blood  pressure.    The 
vagus  nerve,  besides  the  afferent  vagus  fibers,  carries  afferent  or 
sensory  nerves  to  the  vagus  center.     This  can  be  demonstrated 
by  cutting  one  vagus  and  stimulating  the  central  end.  i.  e..  the 
end  running  to  the  brain.    A  marked  slowing  of  the  heart  usually 
results.      By  acting  through   the   vagus  center  and    nerves,   or 
through  the  syini)atlietic  enter  and  nerves,  most  of  the  sen.sory 
nerves  of  the  body,  if    timulated,  can  i)r(Mluce  a  refle.x  .slowing 
or  riuickening  of  the  ..cart  beat.     One  cannot,  however,  always 
predict  exactly  what  result  will  be  obtained.    The  stimulation  of 
the  fifth  nei-ve  in  the  luisal  cavity  or  in  the  mouth  always  causes 
a  reflex  slowing  of  the  heart.    Stimulation  of  the  laryngeal  nerve 
and   the   nerves  of  the   peritonemn   have   a   similar  effect.     It 
is  also  of  interest  to  note  that  the  act  of  swallowing  will  often 
cause  a  decrease  in  the  rate  of  the  heart  through  rcHex  vagus 
action. 

The  relation  of  the  blood  pressure  to  the  rate  of  the  heart  has 
been  noted  in  connection  with  the  cardiac  depressor  nerve 
(p.  187).  Anything  which  produces  au  increase  in  the  pulse 
rate,  other  conditions  Ix'ing  eipial,  will  cause  an  increa.se  in  the 
l)loo<|  j.ressure,  and  this  acts  reflexly  'o  bring  about  a  .slowing 
of  the  heart.  The  reverse  of  tills  is  likewise  true.  In  this  <|uick- 
ening  or  slowing  of  the  heart,  the  vagi  and  the  sympathetic 
nerves  always  act.     In  the  adult  the  normal  rate  of  the  heart 


TIIK   VAS<»Ml)TOR   NKRVKS. 


18!) 


var'u'H  lM'tw«M'ji  6S  aiitl  7(i  |M'r  inimitc.     In  i-hililrni  llic  rati-  is  a 
little  fastiT.  aixl  in  infants  it  may  he  norniaily  \'M)  or  nioff. 

The  Nervotu  Control  of  the  Blood  Veasels. 

During  niust'ular  activity  the  nictaholisni  of  tlic  Ixwly  may  !><' 
incivascd  five  or  hix  timcH.  as  can  be  judKcd  from  tlic  amount  of 
carbon  dioxide  jyivcn  off  by  the  Inn^rs.  Since  this  increase  is  due 
to  the  activity  of  the  nmscles.  it  in  iii'ce>wary  that  thew  obtain 
a  Rrcater  Hupply  of  oxygen,  and  that  they  lie  able  to  rid  them- 
selves of  the  carbon  dioxide  which  is  a  waste  product  of  their 
activity.  Kvery  other  or^^an  re(|uires  an  increased  blwxl  supjily 
when  it  becomes  active,  so  that  blood  has  to  be  divei-ted  from  the 
inactive  to  the  active  tissues,  and  the  least  imp(U'tant  activities 
of  the  body  have  to  be  subordinated  to  tiie  one  which  is  most 
needed  at  the  time  in  <|UeKtioii.  This  action  is  l)rou«ht  about 
partly  by  the  central  nervous  system,  actin^r  tiiroujih  its  afferent 
and  efferent  nerves  on  the  musculature  of  the  blood  vess.ls  of 
the  bwly.  and  partly  by  means  of  chemical  substances  which  are 
produced  at  an  early  stajje  of  the  activity  itself. 

The  Vasomotor  Nerves. — It  was  disecivered  in  the  middle  of 
the  past  century  by  th  French  physiologist,  ("laude  lleriiard. 
that  st'ction  of  the  cei'viCvd  .sympathetic  nerve  in  the  neck  of  the 
rabbi'  causes  a  marked  dilation  of  the  blood  vessels  of  the  ear, 
and  that  during  stimulation  of  the  nerve  with  an  electric  cur- 
rent, the  blood  ves.sels  become  very  small,  and  the  ear  coum  - 
(|Uently  colder.  This  experiment  .shows  that  the  nervous  system 
plays  an  important  role  in  the  control  of  the  flow  of  blood  through 
the  tissues,  and  from  it  many  important  truths  about  the  nervous 
control  of  the  blood  vessels  nuiy  be  deduced.  If  cutting  a  nerve 
will  cause  the  blood  vessels  to  dilate,  and  stimulating  the  same 
nerve  with  an  electric  cui-rent  will  cause  the  vessels  to  constrict 
to  much  less  than  their  normal  size,  it  follows  that  the  blood 
vessels  must  be  normally  held  in  a  state  half  way  between  ex- 
treme dilation  and  constriction  by  stimuli  received  from  the 
nervou.s  system.  The  nerve  fibers  which  carry  the  stimidi,  be- 
cause of  their  power  of  pro«lucing  constriction  of  the  blooil  ves- 
sels, are  known  as  vasoconstrictor  nerve  fibers     Tlx-y  are  cnii!- 


190 


riivsinr/Kiv  poh  dkntm.  sTrnrxTs. 


Ul 


''■1 


paruMf  in  action  to  th.-  acfi-U-iHtor  n.'ivts  to  tin-  li»-ai-t.  Hincr  Htim- 
ulation  of  ritlicr  t.V|H'  of  n.-rv.-  U-iuU  to  |>nHliic.'  an  iiiercaw  in  th«- 
l)loo<l  pr.'MHur.-.  til.-  on.'  \>y  <|iiic|«Miin(f  tho  h.-art  rate  ami  th.- 
other  by  ponstrictinK  thf  blmxl  vt'sufls  and  incn-asiiiK  the  rt'siMt- 
nn(v  to  the  fl«»w  of  bloo*!. 

The  prewncc  of  the  vasooonstrietor  AJhth  in  the  Nvnipathetic 
nerves  is  easily  shown  l»y  the  fact  that  stininhition  of  these  nerves 
to  any  part  of  the  hotly  produces  a  marked  diminution  in  the 
size  of  tile  part  to  which  the  n.-rves  are  connected.  At  the  sani" 
time  there  is  an  increaw  in  the  (^.|u•ra)  bh)od  pressure,  Depause 
the  freedom  of  outflow  of  blood  from  tlie  arterial  system  is  soine- 
wlmt  reduced.  The  lar^re  nerves  which  supply  the  limbs  also 
contain  vasoconstrictor  nerves.  These  are  derived  from  fibers 
coming  from  the  jranglia  of  the  sympathetic  chain  in  the  thorax 
and  abdom.  n  and  .ioininj?  with  the  roots  of  the  spinal  nerves  in 
order  that  the  filx-rs  may'be  distributed  along  with  the  cerebro- 
spinal nnves  to  the  jtart  in  (picstion  (see  p.  277). 

After  section  of  the  spinnl  cord,  th.-  l)lood  vessels  of  the  part 
of  the  hotly  .supplied  with  v)i.s<u'unsti-ictor  nerves  below  the  level 
of  the  .section  of  the  cord,  become  dilated,  and  may  be  constricted 
again  if  a  stimulus  be  applied  to  the  lower  end  of  the  cord.  The 
effect  of  such  a  stinuilus  is  to  inereas*-  the  blootl  pressure,  since 
the  resistance  otfered  to  the  flow  of  1)I(mm1  is  increa.sed. 

The  orjran  in  which  the  changes  taking  i)lace  in  the  blood 
vessels  uutler  various  conditions  can  be  most  easily  demonstrated 
is  the  kidney.  It  is  not  hard  to  enclose  one  kidney  in  an  air- 
tight box.  ami  h\  means  of  rubber  tubing  to  connect  the  box 
with  an  instrument  called  a  tambour,  which  will  record  on  a 
smoked  drum  any  change  in  the  amount  of  air  in  the  box, 
i.  e..  any  increase  in  kidney  vt)lume  will  cause  air  to  pass  out 
of  the  box.  or  the  reverse  in  case  the  kidney  volume  decrea.ses. 
The  instrument  is  called  a  phthysmoffraph.  The  instrument 
applied  to  the  kidney  of  anesthetized  animals  records  each  heart 
beat,  or,  in  other  words,  shows  a  pulse.  Any  change  in  bloo<l 
pressure  will  also  cause  a  change  in  kidney  volume,  but  the 
nature  of  the  c'  ge  will  dej.end  on  the  cause  of  tlu^  change 
of  blood  pressu    .     (Sec  Fig.  26). 


T 


TIIK    VAWtMOTt  H    NKRVKH. 


IDl 


Tin-  vHHoiiiotor  iitrvcH  t»i  .In-  V  iiii-v  iiiul  tlir  alMlutniiial  viHc-cra 
art'  t'(ir  the  iiiimt  part  supinicd  hy  tin-  lowtT  tln»rafir  iicrvfs. 
TIn's*'  syiii|i  thi'tJi!  tilxTs  art-  coiiihiiifd  ami  i-iitir  tin-  aJiil  ii-ii  in 
wliat  an-  known  aH  the  sithimhtm  iirnus,  wliifli  terminate  about 
nerve  eellH  in  a  khi>kI><*»  behind  tiie  stoinaeli,  wliieli  is  ealleil  the 
.S7  tnilioitir  (jiiugUon  of  the  solitv  i>}<  ms.  If  wiiilc  the  normal  vol- 
ume of  th«'  kidney  is  IteiuK  reeordid,  the  splanehnie  nerve  of  the 
eorrespondiiiK  side  of  the  body  is  eut,  the  kidney  will  show  in- 
crease in  volume,  due  to  the  loss  of  the  vasoeoiistrietor  nerve 
eontrol  on  its  vessels.  On  the  other  haii-'  stimulation  e'  the  <Mit 
end  of  the  splanehnie  nerve  leading  tow..  mIs  the  kit  •-.  will 
•iroduee  a  jjreat  decrease  in  the  kidney  volum< .  and  i  arked 
increase  in  the  systemic  blood  pressure,  dm  t<>  ;i  «' minution  in 
the  vohune  of  the  vessels  of  the  kidney  and  of  t''  ■  wlmh-  splanch- 
nic area,  .since  the  si)laiu*linic  nerv  >'ipi>l.v  n.  i  .miy  the  kid- 
neys, but  the  wh' '  '  intestinal  tract  \s  .i.  va.socoiistrii'tor  fibei*s. 

Vasodilator  Nerves. — There  is  another  class  of  efferent  nerve 
fibers  to  the  arteries,  which  are  known  as  the  vastwlilator  nerves. 
When  stimulated  they  briuK  about  an  actual  dilation  of  the  arte- 
rioles, and  allow  a  j»reater  amount  of  blood  to  pass  through  tin 
vessels.  Vasodilator  nerve  fibers  are  found  in  all  the  spiiuil 
nerves,  aiul  they  run  to  the  blood  ves.sels  alonjj  with  the  nerve 
trunks  supplying  the  various  oi-^ans.  Tnlike  the  vasocon.strictor 
nerves,  they  <lo  not  seem  to  be  continually  exerting  an  infiueiiee 
or  tonic  action  on  the  blood  ves.sels.  Hecuse  their  action 
is  hard  to  elicit,  not  so  much  is  kiu)wii  of  their  normal 
functions  as  is  known  of  the  vasoconstrictor  nerves.  In  some 
nerves,  however,  they  j)redomiiiate  and  their  action  is  easily 
seen.  Such  is  the  case  in  the  chorda  tympani,  a  nerve  comiiig 
from  the  seventh  cranial  nerve  and  supplying  the  submaxillary 
gland  with  fibers,  which  when  stimulated  bring  about  an  increase 
in  the  fiow  of  saliva  and  marked  dilation  of  the  blood  vessels  of 
the  gland  (see  p.  41).  Since  the  dilator  filx-rs  offer  more  resist- 
ance to  coUl,  and  live  longer  after  they  are  seven'd  from  their 
nerve  cells  than  vasoconstrictor,  it  is  possible  .  demonstrate  the 
presence  of  these  fibers  in  the  nerve  trunks  of  the  ai-ms  and  legs. 
It  is  only  necessary  to  cut  the  nerves  to  the  extremity  a  few  days 


lf)2 


I'llYsrOI.OOY    F(»K    DENTAIi   STfnFA'TS. 


I' 


h. 


'"'f*>'<'  ♦' -\|)cniiicMt.      Ill  the   iiifaiivvliih'  tlic  vasoponstrictor 

filx'i's  (lie.  iiiid  di!  itors  n-iimiii  alive,  so  that  their  action 
can  be  shown  l»y  takintj  a  volimie  record  of  the  limb  before  and 
diiriiijr  the  stiimilation  of  the  nerve. 

Vasomotor  Reflexes.— In  tlie  same  manner  that  tli<'  heart  is 
iiitlueiiced  liy  afferent  stimuli  reachinjj  cardiac  centers  from  peri- 
plieral  pi.rts  of  the  body,  we  find  afferent  stimuli  affecting  the 
size  of  the  blood  vessels  retlexly  by  way  of  the  vasoii.otor  center 
—located  in  the  medulla  near  the  vagus  center— and  the  vaso- 
motor nerves.     Some  of  the  afferent  imi)ulses  cause  dilation  of 
the  blooti  ves.sels.  wliile  others  cause  constriction.     Perha]>s  the 
most  iiii])ortant  of  the  s<'iisory  nerves,  which,  when  .stimulated, 
jirotluce  a  dilation  of  the  blood  vessels,  is  the  cardiac  depressor, 
which  we  mentioned   in  connection  with  the  afferent  nerves  of 
the  heart.     Jt  will  be  remembered  that  this  nerve  has  .sen.sory 
endings  in  the  left  \entricle  and  in  the  aorta,  and  that  these  are 
stimulated  when  the  blood  i)ressure  in  the  arterial  .sy.stem  reaches 
t(M)  great  a  height  for  the  safety  of  the  individual.     The  stimuli 
originating  in  the  .sen.sory  endings  of  this  nerve  are  carried  to 
the  cardiac  center  and  are  then  transmitted  to  the  heai't  through 
llie  vagus  nerves,    besides  the  slowing  of  the  heart  which  is  thus 
produced,  there  also  occurs  a  dilation  of  the  i)eripheral  vessels 
brought  about   by  the  action  of  the  stimuli  on   the  vasomoter 
center.     This  is  easily  demonstrated  by  electrically  stimulating 
thi'  cardiac  depr.'s,sor  nerve  after  both  vagus  nerves  have  been 
cut  in  the  neck  and  the  retle.x  vagus  action  thus  removed.     The 
fall  of  blood   pres.sur.'  which  is  obtained  under  these  conditions 
is  due  to  an   inhibition  of  the  con.strictor  center  and  a  stimula- 
tion of  the  dilator  (■(■titer  of  the  vasonmtor  nerves. 

Tile  stiiiiulation  of  many  of  the  afferent  or  sensory  nerves  of 
the  body  is  followed  by  a  change  in  the  blood  pressure.  Just 
what  this  change  may  be  it  is  often  impossible  to  predict.  Strong 
sensory  stimuli  of  short  duration  may  j)roduce  a  marked  rise  in 
blood  j)ressiiri'.  the  constrictor  center  iM'ing  the  most  affected. 
On  the  other  hand,  if  the  stimuli  are  very  strong  or  continued 
over  a  long  period  of  time,  the  constrictor  nerves  may  become 
exhaustetl.  as  it  wore,  resulting  in  a  dilation  of  the  arteries  and 


TIIK.    VASOMOTOU    KI'.hM.KXKS. 


193 


H  fall  ill  the  general  l)Ioo(l  pressure.  Like  phenomena  are  often 
seen  following  fright,  pain,  grief,  anil  exeitenieiit.  The  patient 
Iweonies  su<l(lenly  pale,  dizzy,  and  may  faint,  losing  eonseious- 
ness  entirely.  Tiiis  is  due  to  a  fall  in  the  arterial  blood  pressure 
produced  by  a  temporary  inhibition  of  the  va.si.eonstrictor  nerves 
and  perhaps  also  by  a  slowing  of  tlie  heart,  due  to  vagus  stimula- 
tion. If  the  person  bo  standing,  the  blood  naturally  flows  to  tlie 
vessels  of  the  abdominal  viseera  and  dependent  portions  of  the 
body,  and  the  brain  is  tb  "eby  rendered  bloodless.  The  treat- 
ment of  these  eas«'s  is  to  elevate  the  feet  and  abdomen  and  to 
lower  the  head. 

In  ea.se  the  depression  of  the  blood  pressure  slowly  develoi)s 
beea\ise  of  the  gradual  onset  of  fatigue  in  the  vasomotor  and 
other  nervous  centers,  a  eondition  known  as  tmrgiad  shock  suju-r- 
vene.s.  The  treatment  of  this  condition  denumds  plenty  of  air, 
stimulants,  saline  or  blood  transfusion,  and  mea.sures  to  nudn- 
tain  the  body  teini)eraturc. 

The  Pressure  Effects  of  Gravity  on  the  Blood  Flow  var\ 
according  to  the  i)osture  of  the  body.  In  the  upright  position 
the  blood  ves.sels  of  the  feet  support  a  column  of  bl(M)d  of  rela- 
tively great  height,  but  when  the  individual  is  lying  down  this 
ceases  to  be  the  ca.se.  In  spite  of  this,  by  means  of  the  delicate 
adjustments  which  the  nervous  system  can  bring  about  in  the 
heart  and  the  blood  veswls,  there  is  little  difference  in  the  pres- 
sure of  the  blood  in  the  arteries  in  any  position  which  the  i)erson 
may  assume.  The  blood  vessels  and  nerves  soon  lose  this  i)ower 
if  it  is  not  continuously  exercised.  This  is  illustrated  in  patients 
who  hav»'  been  confined  to  their  beds  for  a  time.  If  they  try  to 
walk  or  to  stand  up  suddenl.v.  they  become  very  dizzy  and  may 
faint,  which  means  that  the  blooil  has  left  the  vessels  of  the 
brain  and  is  gathered  by  the  force  of  gravity  in  tlie  vessels  of 
the  deitendcnt  jiarts  of  the  body.  With  a  normal  vasomotor 
mechani.sm.  the  vessels  of  the  feet  and  viscera  would  (juickly 
constrict  to  such  an  extent  that  the  blood  pressure  would  remain 
at  its  normal  height  in  the  vessels  of  the  brain. 

The  fact  that  stimulation  of  sensory  nerves  by  the  gross  meth- 
ods of  the  laboratory  results  in  very  profound  changes  in  the 


194 


niYSIOUKiV    FOR    PENTAL    STrDENTS. 


Mi 
I*  . 


n 


blood  prossuiv  ami  in  tho  velocity  of  the  circulation  of  the  blood, 
suggests  that  normally  the  vasomotor  and  cardiac  nerves  play 
an  imi)ortant  role  in  the  proper  distribution  of  blood  in  the 
various  parts  of  the  body.  Jt  may  be  siii)j>osed  that  normally  the 
nerves  of  th.-  vasculai-  system  function  to  control  the  blood  flow 
tiirough  the  various  organs  according  to  their  resjjective  needs. 
Whenever  the  work  of  an  organ  is  increased,  the  blood  ll.nv  like- 
wise is  augmented  in  the  i)art.  while  in  the  rest  of  the  botly  the 
blood  flow  is  diminished  to  a  greater  or  less  extent.  The  blootl 
supply  is  continually  changing  according  to  the  call  of  the  vari- 
ous tissues  for  blood;  now  the  muscles,  now  the  digestive  organs, 
now  the  brain  demand  more  blood,  and  this  is  supplied  in  tin' 
l>roper  amount  by  the  nervous  syst^-m  conunanding  some  arte- 
rioles to  dilate  and  others  to  constrict. 

Haemorrhagre.— The  action  of  the  vasomotor  )nechanism  is 
beautifully  shown  in  the  cas«"  of  ha-morrhage.  As  blood  is  with- 
ilrawn,  the  vasomotor  nerves  are  .stimulated  by  the  falling  i)res- 
suie  in  the  brain.  This  brings  about  a  more  powerful  tonic  con- 
striction of  tlie  ves,sels  through  the  action  of  vasoconstrictor 
nerves,  the  vascular  area  becomes  smaller  and  smaller  in  size. 
and  less  blood  is  re(iuire(l  to  maintain  the  blood  pre.s.sure.  Be- 
cause of  this  nu'chanism  a  relatively  large  amount  of  bloofl  can 
be  lost  without  affeeting  the  general  blood  pressure  (Fiff  26 
No.  V).  ' 

The  Regulation  of  the  Blood  Supply  by  Chemical  Stimuli.— 

The  calibre  of  the  blood  ves.sels  may  be  influenced  by  other  means 
than  through  their  nervous  mechanism.  Acids  in  very  small 
concentrations  cau.se  a  vascular  dilation.  For  e.xample.  lactic 
acid  and  carbonic  acid,  both  of  which  are  formed  during  nuiscu- 
lar  work,  may  ju-oduce  a  local  dilatation  of  the  blood  ves.sels,  the 
j)henomenon  thus  constituting  an  automatic  nu'chanism  for  deliv- 
ering more  blood  to  a  part  when  it  is  needed.  On  the  other  hand, 
the  secretion  of  the  adrenal  and  of  a  portion  of  tlie  pituitary 
gland  (see  p.  LSI)  i)roduces  a  constriction  of  the  vessels  and 
thus  tends  to  maintain  the  normal  blood  pressure.  Recently  it 
has  been  shown  that  during  i>eriotls  of  excitement  aiul  sensory 
pain  the  amount  of  the  adrenal  secretions  may  be  increysed  and 


ASPHYXIA. 


195 


the  arterial  blood  pressure  raised  as  a  result  of  general  vasoooii- 
strietion.  Beeause  of  its  vasocoiistrietiiig  i)roj)erties,  extraet  of 
the  adrenal  glands  {" ndrrnnUn"  or  "rpincphrin")  is  us«'d 
in  local  anesthetics,  as  in  eooain  solution,  to  prevent  bleeding  and 
to  minimize  the  absorption  of  tiic  eoeain  into  tlie  general  eireu- 
lation  (Fig.  26,  No.  IV). 

Asphyxia. — Whenever  the  amount  of  oxygen  whieli  the  blood 
mu.st  supply  to  the  tissue  falls  below  the  miiiimuin  amount  re- 
ipiired,  a  condition  known  as  asphyxia  develops.    If  tlie  nervous 
centers  are  intact,  any  interference  with  the  respiratory  function, 
as  by  obstruction  of  the  resj)iiatory  pas.sages,  lack  of  ogygen  in 
the  atmosphere,  or  the  i)resence  of  irrespirable  gases  in  the  at- 
mosphere— such  as  carbon  monoxide,  wliich  reduces  the  oxygen 
capacity  of  the  ha'moglobin.  interferes  with  tlie  blood  sui)ply  of 
the  brain — and  will  i)roduce  a  train  of  phenomena  in  which  tiu' 
respiratory  and  circulatory  changes  are  i)rominent.    in  ordinary 
asphyxia  two  factors  may  be  involved,  a  deficiency  of  oxygen 
and  an  excess  of  carbon  dioxide  in  the  blood.     The  i)h(nomena 
following  each  are  cs-sentially  the  same,  and  may  be  divided  into 
three  typical  stages.    In  the  first  stagtN  that  of  hyperpna'a.  tlie 
respirations  are  increased  in  rate  and  amplitude.     This  stage 
merges  into  the  second,  which  consists  of  exaggerated  expiratory 
efforts,  loss  of  consciousness,  .stimulation  of  the  vascular  centers 
in  the  brain  causing  general  vasoconstriction  accompanied  with 
vagus  slowing  of  the  heai1.     Tiie  net  result  is  a  rise  in  blood 
])ressure.    In  the  third  stage,  the  expiratory  eflforts  give  way  to 
slow  deep  inspirations  followed  by  expiratory  convulsions.    The 
pupils  dilate  widely,  the  heart  becomes  very  weak  from  lack  of 
oxygen  and  overwork,  and  death  occurs  from  cardiac  failure. 
The  changes  jiroduced  in  the  resjiiratory  movements,  as  well  as 
those  of  the  vascular  system,  are  caused  by  the  direct  stimula- 
tion of  the  respiratory  (see  n.  220^  and  vascular  centers,  by  ex- 
cess of  carbon  ilioxide  and  by  tlie  lack  of  oxygiii  in  tiie  bloml. 

Nitrous  Oxide. — The  circulatory  and  respiratory  ciianges  ac- 
comi»anying  the  administration  of  nitrous  oxide  gas  are  very 
similar  to  those  produced  in  asjihyxia.  Tlie  asphyxia  produced 
by  the  lack  of  oxygen  and  the  excess  of  carbon  dioxide  in    lie 


196 


PllVSIOLiXn-   FOR   nENTAL   STUDENTS. 


i 


blood  during  gas  anestlu^sia,  stinuilates  the  vasooonstriotor  cen- 
ter, procliicing  a  rise  in  blood  iiressure.  The  nareotie  action  of 
the  gas  depresses  the  inhibitory  effects  of  tlie  vagus  cardiac  wn- 
ter  on  the  heart.  Tlie  lieart  is  therefore  f|uickened  and  tends 
still  further  to  increase  the  blood  pressure.  For  these  reasons  it 
is  not  wise  to  u.se  niiious  oxide  in  the  ca.se  of  elderly  patients 
with  weakened  sclerosed  arteries,  or  in  the  case  of  those  suffering 
from  cai-diac  disi'ase.  When  oxygen  is  given  along  with  the 
nitrous  oxid?  the  asphyxial  phenomena  are  reduced. 

Cocain.— The  effect  of  cocain  injections  on  the  circulation  are 
both  central  and  peripheral,  and  vary  according  to  the  dose  and 
the  individual  susceptibility.  Very  small  doses  generally  cause 
a  slight  fall  in  blood  pressure,  due  to  slowing  of  tlie  heart  from 
stimulation  of  the  vagus.  The  vasomotor  center  is  likewi.se  stim- 
ulated, but  the  resulting  vasoconstriction  does  not  compensate 
for  the  fall  in  pressure  caused  by  the  decreased  action  of  the 
heart.  Mo<leratc  doses  depress  the  vagus  function  and  increas** 
the  heart  rate,  which,  together  with  the  vasoconstrictor  stimula- 
tion observed  in  the  case  of  the  smaller  do.ses.  causes  a  marked 
rise  in  the  blood  pressure.  Large  doses  paralyze  the  vital  centers 
in  the  medulln,  and  a  great  fall  in  blofxl  i)ressure  results.  With 
small  doses  the  res[)irations  are  accelei'ated.  but  in  fatal  doses 
the  respiratory  center  (see  p.  21!))  is  i)aralyzed  and  death  ensues. 


Ib 


CIIArTKU  XXI. 
THE   RKSPIRATION. 

Oxy^t'ii  is  oiu'  of  tlic  t'sseiitial  substaiicfs  rc(|uin'(l  In  cvtry 
living  orfrniiisni.  in  the  c'lls  of  which  it  conibiiics  with  tiic  caiboii 
to  form  carbon  (lioxidc.  and  with  hydrojici)  to  form  water.  All 
the  phenomena  accomi)anying  tiie  supply  and  utilization  of  o.xy- 
gen  and  the  excretion  of  carbon  dioxide  are  included  under  the 
subject  of  respiration. 

In  the  simplest  forms  of  life  the  exchange  of  oxygen  and  car- 
bon dioxi(U'  gas  occurs  directly  witli  the  air.  but  isi  more  complex 
organisms  this  sort  of  exchange  is  impossible  since  t)ract:cally 
none  of  the  cells  composing  the  organism  is  in  direct  communi- 
cation with  the  air.  Some  sort  of  respii-atory  apj)aratiis  becomes 
uwossary,  so  that  each  cell  may  be  supplied  with  oxygen  and 
have  its  carbon  dioxide  removed.  Jn  the  higher  aninuds  this  is 
accomi)lished  through  the  agency  of  th(>"  blood,  which  is  well 
adapted  thus  to  transport  the  oxygen  and  carbon  dioxide,  first 
because  it  contains  chemical  bodies  with  whicii  the  gases  can 
unite,  and  secondly  becaiise  it  comes  in  close  contact  with  tlie 
tissue  ceils  in  the  i)eripheral  portions  of  the  body,  and  with  the 
atmospheric  air  in  tlie  capillaries  of  the  lungs.  The  study  of 
the  resjiiratory  function  therefore  includes  the  mechanism  of 
the  gas  exchange  between  the  ♦issues  and  the  bloo<l.  or  internal 
resi)iration,  and  also  that  between  thi;  lungs  and  the  blood,  or 
external  respiration. 


Internal  Respiration. 

The  energy  vvhicli  the  body  expends  in  the  performance  of  Ihe 
functions  of  life,  including  the  heat  wliich  is  rei|uired  to  main- 
tain the  body  temperature,  is  produced  in  the  cellular  chemical 
reactions,  in  w>^h  the  oxygen  of  the  air  combines  with  the 

197 


198 


niYSIOUKlY    FOR    PENTAIi   STUDENTS. 


JiydroKfii  aiul  carlwii  of  llu-  foodstuffs  to  foi-m  wjitcr  and  carbon 
dioxide  gas. 

Oxidation  in  the  Tissues.— The  actual  mcclianism  whicli 
unites  tlie  oxyjren  with  the  carbon  and  hydrop>n  of  the  food- 
stuffs within  the  tis.sue  ceils,  is  not  entirely  known.  In  spite  of 
the  fact  that  the  processes  of  condmstion  of  hydrocarbon  matter 
outside  the  body  yields  the  .sani.-  end  products  as  the  oxidations 
takinj?  place  within  it.  the  two  i)rocesses  are  not  strictly  analo- 
prous.  An  important  point  of  difference  lies  in  the  fact  that  the 
intracellular  matei-ials— fats,  jiroteins.  and  carbohydrates— arc 
oxidized  with  relativ.'ly  ^jn-at  rai>idity  at  low  temperatui-es 
(88"),  whereas  the  same  reactions  outside  the  body  re(iuirc  a 
v»'ry  high  temperature. 

Let  us  take  as  an  exami)le  the  cell  of  the  yeast  plant,  in  which 
there  is  a  sub.stanee.  under  the  influence  of  which,  the  sutfar 
molecule  Iw'comes  .sjjlit  uj).  at  a  temperature  below  that  of  the 
btMly,  to  produce  cai'jon  dioxide  and  water.  Similar  sul)stances 
are  i)resent  in  the  tissue  cells  of  plants  and  animals;  thev  ar." 
the  ferments  or  enzymes  (see  p.  :{4).  and  they  act  as  catalytic 
agents.  The  function  of  these  bodies  is  to  increase  the  velocity 
of  many  chemical  reactions  which  otherwi.se  proceed  so  slowly 
that  they  may  be  said  in  some  cases  not  to  exist.  A  class  of 
these  substances  is  present  within  the  tissue  cells,  which  at  the 
(h'mand  of  the  tissues  control  the  extent  and  the  velocity  of  the 
union  of  oxygen  witli  the  hydrocarbons  of  the  food.  Such  en- 
zymes are  known  as  oxidases. 

What  evidence  have  we.  how.'v.-r.  that  this  oxidation  takes 
idace  within  the  tissues  and  not  within  the  l)lood  itself?  It  is 
conceivable  that  the  substances  that  are  to  be  oxidized  are  col- 
lected from  the  tissues  by  the  blood,  and  that  the  oxygen  condjines 
with  them  in  this  fluid.  It  is  quite  po.ssible  that  some  oxidation 
takes  place  in  the  boo<l.  for  it  is  es.sentially  a  tissue  and  has 
a  metabolism  of  its  own,  but  this  is  not  true  for  the  oxidation 
which  concerns  the  tis.sues.  since  this  takes  {dace  in  tlie  tissues 
themselves,  as  can  Ik-  shown  by  the  following  fact :  The  blood  of 
a  fi-og  may  b<'  replaced  with  saline  .sol  ition,  in  which  oxygen  is 
di.ssolved    under    pressure,    without    killing    the  animal.'    It  is 


OXIDATION    I.     TlIK    TISSIKS. 


199 


hardly  coiiccivablt'  that  ()xi(hitioii  siiiiihir  to  that  (K'curi-iii>.'  witli- 
iii  tlic  body  can  take  place  in  a  solution  of  sodium  chhn-idc 

Kki.ation  of  ()xn)ATivK  pRoct>;s  TO  Activity.— L'lulcr  ordinary 
conditions  the  hlond  has  a  suitply  of  food  and  oxyscu  sutHicicnt 
for  the  needs  of  the  body.    An  excess  of  either  does  not  intensify 
the  oxidative  prcM-ess.     An  aninud  will  jrive  otT  the  same  amount 
of  carbon  dioxide  in  an  atmosjjhere  of  jiure  oxygen  as  it  will 
under  ordinary  conditions.     This  fact  indicates  that  the  oxida- 
tive jirocesses  are  governed  not  by  the  supply  of  food  or  oxyjien, 
but  rather  by  the  actiud  needs  of  the  tiss\ies.      \  muscle  freshly 
removed  from  th  ■  body  nuiy  Ix'  made  to  contract,  and  will  jrive 
otr  carbon  dioxide  for  some  time  in  the  entire  absence  of  oxygen 
in  the  surrounding  medium.    Another  feature  of  this  experiment 
is  that  for  a  time  after  the  muscle  has  ceased  to  contract,  i*  will 
produce  heat  and  take  up  a  large  amount  of  oxygen.     Indeed 
the  maximal  intake  of  oxygen  and  output  of  heat  often  occurs 
after  the  actual  period  of  work.     In  this  respect  the  mnsde  can 
be  likened  to  a  storage  battery  which  is  charged  by  the  actual 
expenditure  of  energy  and  delivers  .|uickly  the  energy  stored 
up  when  the  circuit  is  closed.     If  the  volume  intake  of  oxygen 
and  output  of  carbon  dioxide  is  measured,  it  will  be  found  that 
the  amounts  are  greatly  increased  during  jM-riods  of  tissue  activ- 
ity.   Kxperiments  have  demonstrated  that  a  muscle  at  full  work 
will  us<'  up  its  owif  volume  of  oxygen  in  ten  minutes.    To  supply 
such  an  amount  of  oxygen  re(|uires'a  very  high  degree  of  effi- 
ciency on  the  part  of  the  distributing  agent,  the  blood. 

PirvsiCAi.  Laws  (Jovkkmnc;  Soi.ition  op  Gases. — A  brief  re- 
view of  the  i)hysical  laws  governing  the  solution  of  gases  in  water 
will  help  us  materially  to  understand  the  mechanism  of  the  traii.s- 
portation  of  oxygen  and  carbon  dioxide  by  the  blood  and  the 
respiratory  mechanism  in  general. 

The  sohd)ility  of  a  gas  in  a  fluid  is  measured  by  the  number  of 
cubic  ci'ntimetres  of  gas  which  one  cubic  centimetre  of  fluid  will 
dis.solve  under  standard  conditions  of  temperature  and  pres.sure. 
Such  a  figure  is  known  as  the  cm-fficient  of  solubility.  For  ex- 
ample, pure  carbon  dioxide  gas  under  standard  conditions  of 
temperature  and  pres-sure  (760  mm.  pri'ssure  and  1.")..')  degrees 


200 


I'lIYSIOUXSV  FOB  DENTAIi  STHDENTS. 


Cent.)  Will  dissolve  to  the  amount  of  one  c.  c.  in  one  e.  e.  of  wat.-r 
ILiuler  like  conditions  only  0.04  e.  e.  of  oxygen  will  be  dissolved. 
1  he  eoeffieient  of  solubility  of  carbon  .lioxide  is  therefore  1.0  and 
01  oxygen  0.04. 

The  amount  of  gas  whieli  will  go  into  .solution  in  water  d.-n.-iuls 
on  three  faetoi-s:  the  temperature  of  the  water,  the  s<,lubilitv  of 
the  gas  in  water,  and  the  pressure  whieh  th."  gas  e.xerts  on' the 
surface  of  the  water.  As  a  rule.the  higher  tl...  tenip..rature  of  the 
water  the  less  gas  will  go  into  solution,  or  in  other  words,  the 
solubility  of  a  gas  varies  inversely  with  the  temperature 

The  pressure  which  a  gas  ex.-rts  on  the  surface  of  a  fluid  is 
expressed  in  terms  of  millimetres  of  mercury.  The  prc^ure  of  an 
atmosphere  is  e(,ual  to  760  mm.  of  mercury  at  .sea  level  and  V,  5 
degrees  temperature.    This  is  known  as  the  standard  barometric 
pressure     If  in  place  of  having  pun-  gases  ov.-r  a  fluid,  a  mixture 
ot  several  gases  be  present,  then  we  find  the  .solubility  of  each  of 
the  ga«.s  varying  directly  with  the  pressure  it  exerts  on  the  sur- 
face of  the  fluid.    Su,.pose  that  in  place  of  .-xposing  a  cubic  centi- 
nietre  of  water  to  oxygen  at  760  mm.  pressure,  we  exi)ose  it  to 
oxygen  at  a  pressure  of  152  mm.  n.ercury-tl.,.  normal  pressure 
of  oxygen  in  the  air  1;5  of  an  atmasphere)-it  would  aksorb  1/", 
of  .04  c.  c.  or  .008  c.  c.  of  oxygen.    The  pivsence  of  other  gases 
does  not  enter  into  consideration,  for  accor.ling  to  Dalton-IIcn- 
ry  s  law,  when  two  or  more  gases  are  mixed  together,  each  of 
them  produces  the  same  pres.sure  as  if  it  .separately  occupied 
the  entire  space  and  the  oth.r  gases  were  aksent.    Wh;n  the  fluid 
has  taken  up  all  the  gas  it  can,  an  e.)uilibriun.  becomes  estab- 
lished between  the  gas  in  the  atmosphere  an.l  the  gas  within  the 
fluid.    The  pr..Nsure  which  the  gas  in  the  fluid  exerts  on  the  gas 
m  the  atmosphere  is  known  as  the  tension  of  the  gas,  and  e.,uals 
the  pressure  of  the  gas  in  the  out.side  atmosphere  to  which  it  is 
exposed.     This  can  be  easily  measured. 

Since  the  pressure  of  the  oxygen  in  the  air  ,n  the  lungs  is  less 

han  that  in  the  (Hit.side  atmos,,here,  it  is  apparent  that  if  the 

blood  should  carry  the  same  amount  of  oxygen  as  water,  the 

amount  would  be  very  s^nall  indeed.    Analysis  of  the  amount  of 

oxygen  m  arterial  blood  shows  that  it  contains  40  times  the 


Il.KM()aiA)BIN. 


•_»()! 


amount  iicr  f.  c.  that  wat«'r  vnii  dissolve  uikUt  like  romlitioiis. 
For  oxamplf,  U-t  us  iiuaghu'  human  blood  to  Im-  water.  It  wouM 
earry  then  only  1  -^O  oi  the  volume  of  oxyjren  that  it  does,  and 
the  body  would  need  the  vaseular  system  of  an  eh-phant  or  tlie 
tissues  of  a  rabbit  in  order  to  obtain  as  mueh  oxygen  as  normally 
is  supi)lied  by  the  blood.  Therefore  it  is  obvious  tliat  the  laws 
for  simple  solutions  eaii  apply  oidy  in  a  sliyht  <le«ree  to  the 
jjases  in  the  blood.  They  would  aeeount  at  the  most  for  only  0.7 
per  eeut  of  the  total  oxyp-n  and  2  per  eeiit  of  the  earbon  dioxide 
found  in  the  blood. 

Haemoglobin. — The  extraordinary  ability  of  tiie  blood  1o 
earry  oxyjfen  and  earbon  dioxide  lies  in  the  preseiiee  of  sub- 
stanees  eapable  of  ehemieally  u/iitiu},'  and  thus  storing  up  lar«e 
amounts  of  tlie  Rases.  The  iron  eontaininy  [)rotein  sultstance 
ealled  ha-mojrlobin,  found  in  the  red  bl<K)d  eells  carries  the  oxygen, 
and  tl;e  alkalies  and  proteins  of  the  blood  earry  most  of  the  ear- 
bon dioxide.  Analysis  of  samples  of  arterial  and  venous  lilood 
^jives  the  following  averajre  fiffures.  whieh  represent  llie  voliniies 
of  the  gas  found  in  one  hundred  volumes  of  lilood. 


OxyBen 

1(10  vol.  arterial  blood  contains 20 

100  vol.  venous  blood  contains 10-12 


CO.  NitroRon 

40 "  1-2 

45-50  1-2 


The  sm.ill  amount  of  nitropen  present  in  the  blond  in  s|)ite  of 
the  larpe  jiereentajre  found  in  the  atmosphere  (4  .'>  i.i  ilie  baro- 
metrie  pressure  bein<;  due  to  nitrogen)  is  due  to  the  absence  of 
any  ehemieal  body  within  tiie  blood  plasma  which  will  unite  wilii 
nitrojren.  Of  the  20  volumes  per  cent  of  oxyjien  found  in  arterial 
bloo<l  only  0.7  jier  cent  is  in  .solution  in  tiie  jilasma. 

Rklatkkn  of  Oxyckn  to  II.K.M(Kii-oBiN. — lu  order  to  under- 
stand the  attinity  of  oxygen  for  ha'moglobin,  we  nnist  investigate 
the  v-arious  conditions  which  favor  the  union  of  liaMuoglobin  with 
oxygen  and  the  break-down  of  the  resulting  o.xygen  compound. 
oxyha'Uioglobin,  into  oxygen  and  ha-moglobin.  Equal  (piantities 
of  purr  hvmoglobiii  suliitiou  are  placed  in  a  series  of  glass  ves- 
sels containing  variable  iiuantilies  of  o.xygen  mixed  with  nitrogen 


202 


l'HYSlnl.(HIY    Fob   DKNTAr,    STfOKNTS. 


'^ 


lit  afiiKwplH'ric  prcsHun'.  After  slwikiiiK.  tlic  soliitioim  arc  rciiiovt'd 
iind  tilt'  Hiiiouiit  of  oxyRfii  in  t-Hch  sample  is  measured. 

The  liH-nioKlobin  solutions  in  the  tubes  eontaiiiiiiK  h  partial 
pressure  of  oxy>?en  which  is  within  two-thirds  of  that  present  in 
air  (iM'twecii  !»0  and  l.'»2  mm.  of  mercury)  are  all  almost  satu- 
rated with  o.xyjjeii.  In  other  words,  at  these  pres.siires  the  hu-mo- 
Klohin  i-xists  entirely  in  the  form  of  oxyliji'inoglobiii.  In  the  tube 
containiiiKT  one-half  the  pressure  of  oxyjfcn  in  air  (i.  e.,  almost  7<) 
mm.  Hg.;.  the  ha-moKlobin  solution  is  !»0  \wv  cent  saturated.  M 
about  one-fourth  the  norinal  oxygen  j)ressuie  in  air  (i.  e..  40  mm. 
Hr.),  it  is  a»M)Ut  84  per  cent  saturated.  At  lower  partial  pivs- 
Hures  of  .).\ygen,  the  ability  of  Irn'moglobiii  to  unite  with  oxyjfii 
very  rapidly  decreases. 

From  these  obsci'vatioi'.s  we  must  conclude  that,  as  the  jires- 
sure  of  oxygen  in  contact  with  the  luemoplobin  .solution  increases 
above  zero,  by  •rraded  stages,  the  amount  of  oxygen,  per  unit  of 
increase  of  oxygen  pressure,  that  combines  with  lucmoglobin  at 
low  j)rcs.sures  is  large,  but  liecoiiies  relatively  less  at  higher  pres- 
sures. Or.  conversely,  if  the  lucmoglobin  saturated  with  oxygen 
!)♦■  subjected  to  decreasing  oxygen  jiressure.  the  combined  oxygen 
is  set  free  at  fir.st  slowly  and  then  more  rapidly. 

If  the  oxygen-coiiibiiiing  jmwer  of  hlaotj  be  investigated  in  ex- 
actly the  same  way  as  described  above  and  the  results  compared 
with  those  of  a  pure  liaMiioglobin  solution,  a  marked  difference 
will  be  observed.  At  low  pressures  the  oxygen  is  more  easily  re- 
leased from  the  lucmoglobin  of  the  bloo<l  than  from  piir(>  .solu- 
tions of  ha-moglobin.  An  iiKpiiry  into  the  cause  of  this  difference 
has  revealed  the  following  facts.  The  rate  at  which  oxyhremo- 
globin  breaks  down  into  oxygen  and  ha-mogloVin,  depends  on 
other  factors  besides  oxygen  pressure.  These  are:  (1)  tempera- 
ture, (2)  the  presence  of  inorganic  salts,  and  (:5)  carbon  dioxide 
or  other  weak  acids  in  the  blood.  If  ha'moglobin  be  dissolved  in 
a  s,!liiie  .solution  containing  the  same  concentration  of  inorganic 
salts  as  is  f(mnd  in  blood,  it  will  take  up  oxygen  in  a  manner 
somewhat  similar  to  blood  under  like  oxygen  pressures.  The 
similarity  will  become  perfect  if  the  saline  .solutions  of  ha'mo- 
globin be  subjected  to  the  same  pri'ssure  of  carbon  dioxide  as  that 


II.KM<HII.OIIIN. 


2():{ 


pn-w'iit  ill  \]h'  KHinplf  of  M»mm1.  that  is,  provided  the  tniipfratiiri' 
iH  the  saiiu"  in  tin-  two  caHi-H.  Of  tin"  curvi-s  nIiowii  in  Vig.  '21,  n 
rcprcsiMitH  tlu"  ili'trrw  of  dissociation  of  oxy^ft-n  from  pure  oxy- 
lia-niotrlohin  solution  at  varying  oxyjfiii  |>r«'ssun's;  /».  tli.'  nuMlifi- 
cation  in  tlu-  tlt'Krcc  of  tin-  association  produced  by  the  presence 


100 

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A       tn 

Fin.     -l- 

Ordlnatt-s— I'.ivoiitiiKf   Hiituiation   of   ha'inoKlol'in    with   oxvK.  ii. 
VbsiisHH.-— Tnisiiin  of  oxyKcn  in   mm.  of  meii'ury. 

Curve    A— IX'Kiv..    of    saturation    of    pure    ha-moK in    solutionw    at    varyini; 

l)rfsaures. 
Curve   B-Mo.ll«»ation   of   .l.'Kr.e   .if   saturation   lause.l    l.y   presence   of  sallK 

in   tlie   lilood. 
Purve  r— Kffecl  of  20  mm.  C"Oj  pressure  on  almve  solution. 

Curve    U— The  saturation   cur.e   in   normal    bioud  at    H»   mm.   Ci*rl>..„   dioxi.le 
pressure. 


■''I' 


201 


I'llYSIOl^HlV   FOR   DENTAL   sTrilENTM. 


|!;l 
U 


of  thf  Wilts  of  th."  hlmMJ;  <  and  «',  th.-  .fT.-ct  of  (■ail>oii  <lioxi<l<- 
|tr.'H«ui-«'H  (III  the  oxyKcii  contfiit  of  t\w  hu'iiioKliiiiiii  in  a  Huliiic 
Holutioii;  hikI  (I  is  the  iliswociatioM  ciiivf  of  noniml  blood  with  a 
nirhoii  dioxid»'  tcimion  of  40  iiini. 

The  cfr.rt  of  carbon  dioxide  in  of  sjuH-ial  iiittn'st.  It  is  m-tii 
tliat  the  jcrt-atcr  the  eoiiwiitiation  of  t-ailwii  dioxid.-.  the  more 
ivadily  is  the  oxy^.<ii  dlMsociatcd  fr.wii  the  oxyba-iiiojrhiltiu.  Thus, 
at  an  oxyj^-n  pi-cssurf  of  20  mm.  of  m.Tcury.  th.-  amount  of 
oxyha-niOKlobiii  form.-d  is  iu.:>  p.-i-  .•cut  of  th.-  total  lucmoKlobin 
at  a  carbon  dioxide  piVHsiirc  of  ,")  mm.,  whereas  at  a  pressure  of 
40  mm.  of  carbon  dioxide  the  amount  of  o.xyha-mofflobin  is  only 
2!>..")  jier  cell*.  InaMiiucli  as  the  amount  of  carbon  .lioxide  is  coii- 
stHiitly  chai./ing  in  arterial  and  venous  lilooti,  the  iiresciice  of 
thi.vi  tins  would  seem  to  Ik'  an  important  factor  in  the  eonti-ol  of 
the  oxidiition  or  thr  dissociation  of  the  ha-iiioKlobin  compounds. 
At  any  rat^s  it  would  help  to  account  for  the  ease  with  which 
ox.vffen  is  bn.keii  from  the  oxyha'inoKlol.in  molecule  in  the  ea|.il- 
laries  which  are  imbe.hled  in  the  tis.siies  where  the  carbon  di(.xide 
is  formed,  and  its  pressure  is  correspondingly  lii^h. 

The  Mechanism  of  the  Respiratory  Exchange.—Tlu  oxygen 
in  the  alveoli  or  air  pa.ssajjes  of  the  lungs  comprises  about  14  to 
ir»  per  cent  of  the  total  air.  an<l  exerts  on  the  cells  of  the  respira- 
tory ei»ithelium  a  pressure  of  about  100  mm.  mercury,  more  or 
les.s.  Venous  blood  when  it  reaches  the  lungs  contains  about  50 
per  cent  less  o.xygeii  than  docs  arterial  blood,  and  can  take  u|) 
from  6  to  8  c.  c.  of  o.xygen  for  every  one  hundred  e.  c.  of  blood. 
If.cmoglobin  solutions  are  almo.st  completely  .saturated  with  o.xy- 
gen  at  pre.s.sures  of  o;...>?en  much  l.-ss  than  100  mm.  of  mercury. 
There  are,  tlii-refore,  very  favorable  conditions  in  the  lungs  for 
ha-moglobin  to  take  up  oxygen  from  the  air.  It  must  be  under- 
stood, however,  that  the  luemoglobin  does  not  obtain  oxvgen  di- 
rectly from  the  air.  The  ha'moglobin  is  held  in  the  bIoo<l'  corpus- 
cles which  are  floating  in  the  blood  plasma.  Jietwcen  the  plasma 
Jind  the  air  in  the  lungs  lie  two  thin  meMd)rane.s,  the  capillary  wall 
and  the  wall  lining  the  air  sac  of  the  lung.  The  oxygen  must  first 
be  dis.solved  by  the  tluid  in  the  lung  epitheliuni:  from  this  th<- 
cells  of  the  capillary  walls  take  oxygen,  and  the  plasma  in  turn 


ItKSIMKATtlKY    I.XCll  \NIIK. 


•_»o:. 


tnk»'«  tlif  oxyKfii  fi-oiii  tlw  capilliirv  cells.  'T\\r  itlasiiia  loses  tln' 
oxyKcii  tliiiH  obtaiiu'tl  heeaii-se  the  lni-iMonlt>l)iii  is  very  irreedy  for 
oxyjjiii.  There  in  awonliiiKly  a  tlitfiTt'iice  in  the  oxyp-ii  |>reH8ure 
in  the  plasma  of  the  eapillaries  of  the  liiiijrs.  siirtieient  to  aeeoiiiit 
for  th«'  abHorption  of  oxy«eii  hy  the  h«'nio>flol>iii  of  t'le  hhioil.  The 
hlood  leaving  the  Umtts  is  delivered  into  the  left  ventricle,  from 
which  it  is  distrihuti-d  over    the    body.     Since    oxidation    takes 
place  within  the  tissue  cells,  oxy>f<-n  is  bein«  continually  called 
for,  nnd  the  lymidi  Hurroun<linK  the  cells  must  continually  jrain  a 
frt'sh  supply  of  oxygen  from  the  plasma  of  the  blood.    This  re 
duces  the  tension  of  (txygcu  in  the  plasma  and  causes  an  evolution 
of  oxyjT"'"  from  the  oxylunnojrioltiu.  which  is  taken  up     y  the 
plasiiui  t(^  1m-  pasw'd  on  to  the  lymph  and  then  on  to  the  cell. 
There  is  thus  a  desceiidinjr  wiile  of  pressure  or  tension  of  oxyjieu 
from  the  air  of  the  lini^s.  where  its  pres.surc  may  amount  to  100 
nun.  of  mercury,  until  it  reaches  the  tissue  elements,  where  the 
pressure  nuiy  t»e  considered  zero.    V'   ler  ordinary  <-onditions  the 
circulation  is  fast  enough  to  proliibit  the  comphte  ieducti(Ui  of 
the  oxylm-mo«iobin.     In  case  it  is  not,  or  in  cise  lli.-  o.xytreii  su|>- 
ply  is  short,  the  phenomena  of  asphyxia  ilevelop  (see  p.  llt.'n. 

Kkfkct  ok  (".'.rhon  Dioxiuk  <>\  t>xvii.K.M.M!i.(tiu\. — As  a  result 
of  the  oxidative  changes  which  take  place  within  the  cells,  carbon 
dioxide  is  i)n)duced,  and  the  tension  of  ti  ^s  >ras  rises  in  the  tis- 
sues.    It  will  be  remembered  iti  the  di>M'Hssu)n  of  the  dissociation 
of  oxyha'inojilobin.  that  the  et!Vct  of  increased  tensions  of  carbon 
dioxide  is  to  increasr  the  rate  of  reducfioii  of  (ixyluenu)f,'lobin  into 
oxy^'en  and  hu-moRlobiii.     Since  there  is  a  hijih  tension  of  car- 
bon dioxide  pi-esent  in  the  tis.sues  and  at  the  site  of  the  capil- 
laries,  the   effect    on   the    reduction   of  oxyha-mo-iiobin    is   very 
marked,  and  has  a  fireat  influence  on  the  rate  at  which  oxygen  is 
supplied  to  the  tis.sues.     Just  as  there  is  a  desceiidinji  pres,sure 
of  oxygen  from  the  air  iu  the  lunsrs  to  the  cell,  so  is  there  a  dc- 
cnase  in  pressure  from  the  carbon  dioxide  in  the  cells  to  the  air 
of  the  luuKs.  This  gas  therefore  parses  through  tlu'  lymph  to  the 
plasma  and  out  of  the  i)la.sma  through  the  juilmonary  epitheliuin 
bv  tlie  simple  proce.vs  of  diffusion. 

The  Exchange  op  Carbon  Dioxide.— Analysis  of  venous  blood 


206 


I'llYSKlLOCV    FOK    I)i:\T.\r.    STIDENTS. 


m 


shows  tliat  100  c.  v.  contains  alwut  45  to  r)0  c.  o.  of  carbon  diox- 
ide, and  that  th.-  jjas  ,.x,.rts  a  prcssun-  or  tension  of  al)<)ut  40  nun. 

mercury,  which  is  c.|ual  to  about  five  i)ei nt  of  iin  atinosplierc. 

Now  water  will  dissolve  under  tiiese  conditions  about  2K,  c  c  of 
earbon  dioxide  jn-r  100  c.  c.  This  woui.l  leave  tlie  nicm't  of  the 
carbon  dioxide  of  tlie  blood  unaccounted  for.  in  case  the  blood 
lias  the  same  solvent  i)ower  foi-  the  jras  that  wat.-r  has.  The  rest 
of  the  carbon  dif.xidc  then-fore  must  be  accounted  for  as  beinfi 
in  chemical  cond)ination  with  the  constituents  of  the  jdasma  and 
corpuM-les.  Th.-  major  j)art  is  probably  held  i,,  the  form  of 
sodium  carbonate  and  bicarbonat.-,  the  remain<l..r  being  combined 
with  the  i)roteins  of  the  plasma  and  the  red  corpuscles.  The  most 
satisfactory  explanation  of  the  manner  in  which  carbon  dioxid.' 
IS  dissociated  from  the  above  mentioned  comi)minds  in  the  blood, 
IS  that  then-  are  substances  in  the  i)lasma,  such  as  the  blood  pn)- 
teins,  which  act  as  weak  acids,  and  frradually  drive  off  the  carbon 
<lioxid..  when,  as  in  the  air  in  th,-  hmss.  its  escape  is  renden-.l 
easy  by  a  lowen-d  carbon  dioxid.-  pressure  outsid,-  the  plasma. 


Iff 

55     ■■  ( 


("IlAl'TKU  XXII. 

TIIK  HKSI'IKATIOX  (<"(>iif(l). 

The  External  Respiration. 

Anatomical  Considerations. — Tin-  coiistjnit  call  of  the  1  issues 
for  oxygen  and  tlu'  foniiatioii  of  the  waste  jjas.  carbon  dioxide, 
demands  a  nicclianisni  l)y  whicli  the  blood  can  contin\ially  renew 
its  sui)ply  of  oxygen  {"iid  excrete  its  excess  of  cirbon  dioxide. 
This  cxchangre.  as  we  have  .seen,  is  eti'ected  in  the  lunf,'s,  which 
are  built  up  in  tlie  followinjf  way: 

The  nasal  and  oral  cavities  lead  to  the  i)harynx.  from  which 
open  two  tubes:  one  ])ostcrior.  the  d-sophaftus.  jroin>r  to  the  ali- 
mentarv  tract,  and  the  other,  anterior  the  trachea.  j,'oinj,'  to  the 


Kis,'.    2S. — ni.iniaiii    "f   structun 
(■hiole.«   iiiid   alveoli. 


>f   luiiBs   .^linwiii;;'   liiiynx,    Inoiii'hi.   Imiii- 


Innijs  (Fifj.  2S).  At  the  befrinninp  of  the  trachea  is  |)laeed  the 
larynx,  or  the  voice  box,  the  openinjj  of  which  is  tjuarded  by  a 
flap  of  tissue,  the  epifilottis.  Within  the  larynx  are  the  vocal 
cords.  The  trachea,  or  windpipe,  is  a  relatively  laryre  tube,  about 
four  and  one-half  inches  long,  which,  after  its  entrance  into  tlie 
thorax,  divides  into  two  tubes,  the  bronchi,  each  of  which  subdi- 
vides again  and  again,  the  branches  gradually  growing  smaller 
until  they  are  mere  twigs,  and  are  known  as  bronchioles,  or  small 

207 


208 


l"IIYSI()r,(KiY    FOR    HKNTAI,    STIDEXTS. 


broiiclii.  The  hini.-ii  of  tli."  tni'Moa  and  bronclii  is  niaiiitaiiiod 
patent  1»>  cailila-rf  l>latfs,  which  arc  imlx-dih'd  in  tiic  walls  of  the 
tulh's.  The  l»foiichiolcs,  however,  liavc  no  such  plates,  their  walls 
heinfj  conijmsed  of  fibrous  and  elastic  tissue,  in  which  is  a  layer 
of  smooth  muscle.  The  whole  syst.'Ui  of  tubes  is  lined  with  a 
layer  of  ciliated  epithelium. 

The  lironehioles  terminate  in  wide  air  .sacs  or  cavities,  the  in- 
fundibuli,  from  the  walls  of  which  extend  numerous  minute  cavi- 
ties, the  alveoli.  The  walls  of  the  alveoli  are  very  thin  but 
stroiiff.  and  are  composed  of  a  layer  of  elastic  tissue  lined  with  a 
sin«,'le  layer  of  flatt.'ticd  epithelium.  It  is  estimated  that  the  epi- 
thelial surfaces  of  the  alveoli,  if  they  were  s])reail  out  on  a  flat 
surface,  would  cover  about  1.000  sipiare  feet.  Such  a  lai'fje  area 
exposed  to  the  air  of  the  huifis  oflTers  the  best  of  facilities  for  the 
ra|)id  exchanjje  of  the  respii'atory  jjases.  and  in  fact  the  walls  of 
the  alveoli  are  the  true  respiratory  membrane  of  the  lunfj.  for 
throuffh  them  the  exchanfre  of  <rases  between  the  iiir  and  the 
blood  takes  j.laee.     i'.elow  th.'  ejdthelial  cells  of  the  alveoli  lie  tlu' 

capillaries  of  tlic  |>ulmonary  artery  in  a   rejjrular  shwork:  so 

numerous,  indeed,  aiv  they  that  I'ach  individual  erythrocyte  is 
able  to  come  in  ch.se  contact  with  the  air  in  the  alveolus,  separ- 
ated oidy  th.'refrom  by  the  liriinjr  of  the  alveolus,  the  wall  of  the 
artery,  and  the  plasma  of  the  blood.  This  arran>;emcnt  Tiiakes 
possible  the  I'apid  e\ehan!.'e  of  jrascs  which  must  take  place  with- 
in the  Iun<rs. 

The  two  luiifrs  in  company  with  the  heart  occuj)y  the  thoracic 
cavity,  which  is  bounded  above  and  on  the  sides  by  the  ribs  and 
their  attached  tissues,  atul  below  by  thediaphrafrm.  a  muscular 
sheet  of  tissue  which  divides  the  body  cavity  into  a  thoracic  and 
an  abdominal  imrtion  (  Pijj.  2'.)).  The  lunjis  are  suspended  at 
their  roots,  which  are  composed  of  the  trachea  and  the  jiulmonary 
blood  vcs.sels,  and  they  lie  free  in  the  thoracic  cavity  in  close  a[)- 
|)osition  with  the  walls  of  the  thorax.  Coveriiifr  the  outside  of 
the  luiifys  and  the  inside  of  the  thoracic  cavity,  which  is  in  con- 
tact with  the  luufrs.  is  a  thin  endothelial  membrane  known  as  tlie 
jtleura,  the  surface  of  which  is  kept  moist  by  a  .secretion  of 
lymph.     This  smooth  membrane  allows  the  surface  of  the  lungs 


THK    MKCMANIf^M    OF    BKKATIIINli 


200 


to  move  i.isily  over  tlic  iiiiicr  surfacf  of  th<'  thorax  duriiij;  llif 
cliiiiiffcM  .1  tilt"  size  of  tin-  cavity  wliicli  a('('()ini>aiiy  the  n-spiratory 
inovi'iiifiits. 

Mechanism  of  Breathing.— Nornial  hn-atliiiifr  lias  the  olOcct 
of  briiifiiiifr  about  a  constant  renewal  of  air  in  the  luiifrs.  and  it 
is  etTeeted  by  niovenieiits  of  the  thorax  and  dia|)liratrni.  When- 
ever the  cavity  of  the  thorax  is  eidar^'cd.  as  in  the  act  of  inspira- 
tion, the  hinfrs  must  increase  in  size  to  fill  the  space,  and  air  is 


I'iK.   2:". —Til.'  iicisitiim  nl   Ow  liiiiKs  in  ihf  thmux.      (  T,   Wimiiilc  'I'liild  ) 

pushed  into  the  respiratory  tubules  and  the  air  sacs  by  the  pres- 
sure of  the  outside  atnuisphere.  At  exi)iration  t!i(>  reverse  takes 
l)iace.  and  the  air  is  expelled.  A  very  fjood  c()ncei)li()n  of  the 
mechanism  by  which  this  is  brought  about  nuiy  be  had  by  refer- 
ei.'-e  to  Fig.  :{().  Any  increase  in  size  of  the  bottle,  as  by  i)uHing 
■  ■own  the  bottom  ru])lM'r  meiubrane,  will  cause  air  to  expand  the 
rubber  sacs  coming  in  by  the  tube  passing  through  the  cork  of  the 
bottle.  When  the  size  of  the  cavity  is  ilecreased  by  releasing  the 
meinbi'ane,  the  revei'se  takes  jdace  and  air  is  exi)el!ed  from  the 
rubber  sacs. 

With  every  in.spiration  the  thorax  is  increased  in  size  in  all 


ft  r 


210 


IMlVSIOI.CHiV    FOR    DKNTAI,   STIDKNTS. 


(liaiiit'tcrs,  from  almvc  (lowiiwiinls  l»y  the  contnictioii  of  the 
(li«l)iiraKm,  and  in  tlic  transverse  diameter  by  tlie  movement  of 
tlie  rilw. 

TiiK  Part  Pi.avkd  bv  tiik  DiAi-iiRAcai.— The  diai>liragm  is  a 
circular  sheet  of  miisele  whieh  .livides  the  body  eavitv  into  two 
compartments,  the  u|)i)er  l)ein^  th.-  thorax,  th,'  lower  the  abdom- 


li'  -^ 


FiK.   30.— H.-rin>rs  iiDi.aiatus  f„r  denionstratiMK  the  action   of  the  resnirn- 

.7r„\'r'\  '^^*'  '^'TV  '■''"'•'■«"'••"'  '->•  "   '"'«"-■  th..  diaphraKm  by  a  sheet 
f      UM...  •    forn.mK    .t.s    l,o„o,„,    the    tra.hea    hy    a    tube    „a«.si„^    through    the 

1  ':  h  ."  IT"  !';'  '"■"  ''"'  '"'""'■  '"""  '  '*''"  "'"-  "f  •■"•^'-'-  tuhint, 
COS.,.,,  the  bottle.  'lh>«  ,e|,.esent.s  the  h.-art.  The  action  of  the  dla,.hra<m 
pumps  a,r  ,n  and  out  of  the  lun»..s  and  water  through  the  heart.  The  un.^^ 
and  heart  are  thin  rubber  baKs.      (  Fro„,    Baird  an,l   fo.-.s  catalogue.) 

inai  cavity.  In  the  iii)|)er  cmupartment  are  the  lungs  and  heart 
witli  the  aceomj>anyins  blood  vessels  and  air  passages.  The  ab- 
(loniinal  cavity  contains  the  di-.-stive  organs  and  glands,  as  the 
hvcr,  kidneys,  spleen  and  ivproductive  organs.  The  perii.heral 
edges  of  the  diaphragm  are  iittached  to  the  lumbar  vertebnc  at 
the  back,  to  llie  lower  border  of  the  libs  on  the  sid.-s,  and  to  the 
tip  of  the  sternum  in  front.     The  muscular  fibers  radiatt'  to- 


TlIK    MECHANISM   OF   BRKATllINO 


211 


wards  the  centor  iiiid  t'nd  in  a  ttMidinotis  sheet  of  tissue  ealled  tlie 
central  tendon  of  the  diaplirajjin.  When  these  filters  are  relaxed, 
tile  dia|)hrajrni  is  pushed  u))  into  the  thoracie  eavity,  foiinins  a 
dome-shaped  areh.  This  is  eaused  by  the  pressure  of  the  ahdoini 
nal  organs,  supported  by  the  nmseular  walls  of  the  abdomen,  on 
its  lower  siirfaee,  a  suction  pressure  on  the  up|)er  surface  of  the 
diaphragm  iM-ing  maintained  by  the  natural  tendency  of  the 
lungs  to  contract.  The  central  tendon  is  pulled  downwards  and 
the  arched  dome  is  flattened  on  contraction  of  tiie  diaphragm, 


Fi»r.    31 
1.    .xpii'Ht 


-ratii   to    show    mfivemi-nt    of   diaphraKni    (iuriiiK    icspitiilioii : 
normal    ins|>iratioii  ;    Ml.    fori  ni   in-spiration. 


thus  increasing  t!ie  size  of  the  thoracic  cavity  (Fig.  111).  An- 
other result  of  the  lowering  of  the  diai)hragm  is  the  slight  i)ro- 
trusiou  of  the  abdomen  due  to  the  pressure  exerted  on  the  vis- 
cera. This  type  of  .breathing  is  therefore  known  as  abdominal  or 
diaphragmatic  breathing. 

TiiK  Part  Pi.aved  by  tiik  Thorax. — The  action  of  certain 
muscle-s  attached  to  the  ribs  also  produces  an  enlargement  of  the 
thoracic  cavity.     Kach  pair  of  corresponding  ribs,  which  arc  ar- 


212 


PHySIOI/X5Y   FOB   DENTAL   STl'DENTS. 


ticulfitcd  posteriorly  witli  the  vcrtcbml  column  and  anteriorly 
with  the  Ntermun,  forms  a  rinj?  directed  ol)li(|Uely  from  behind 
forwards  and  downwards.  Any  muscles  whose  action  would 
l)ring  about  a  raising  of  the  anterior  ends  of  the  ribs,  would 
therefore  lessen  the  obli(|ue  position  and  increase  the  distance  be- 
tween eadi  i)air  of  ribs,  and  also  add  to  the  anterior  posterior 
diameter  of  the  thorax.  Moreover  each  rib  increases  in  length 
from  above  downwards,  and  as  the  ril>s  are  raised,  the  lower 
longer  rib  occupies  the  j)lace  i)reviously  held  by  its  shorter  neijjli- 
bor.  This  movement  therefore  causes  the  dome  or  a})ex  of  the 
thorax  to  become  more  flat  and  broad.  Moreover  the  lower  ribs 
are  so  articulated  with  the  spinal  column  that  they  exhibit  an  up- 
ward rotary  movement,  which  i-esembles  that  made  by  a  bucket 
handle,  and  which  increa.ses  the  lateral  or  transverse  diameter 
of  the  thorax. 

The  iimscles  which  are  responsible  foi-  the  insi)iratory  eleva- 
tion of  the  ribs  are  mainly  the  external  intercostals,  aide«l  by 
other  muscles  of  the  thorax,  some  of  which  are  called  into  use 
only  when  very  powei'ful  respiratoi-y  movements  are  necessary. 

Normal  expiration  is  almost  entirely  a  passive  act.  The  re- 
coil of  the  stretched  elastic  tissue  of  the  lungs,  after  the  in- 
spiratory muscles  have  ceased  to  act,  returns  the  diaphragm  and 
thoracic  cage  to  tlie  expiratory  position.  This  is  aided  somewhat 
by  the  actions  of  the  internal  intercostal  nniscles  which  lower  the 
ribs.  By  increasing  the  size  of  the  thoracic  cavity,  inspiration 
causes  a  corresponding  increase  in  volume  of  the  thoracic  organs: 
viz.,  the  lungs  and  the  vascular  structures,  because  the  thorax  is 
a  closed  cavity,  so  that  when  it  expands  it  must  either  produce  a 
vacuum  between  tlie  organs  which  fill  it  and  its  own  walls,  or  the 
volume  of  the  organs  nuist  increase.  It  is  the  latter  process 
which  mainly  occurs,  the  result  being  that  air  is  pushed  into  the 
lungs  by  the  atmospheric  pressure  whenever  the  thoracic  cavity 
is  increased  in  size. 

TiiK  Movements  of  the  Lungs. — The  changes  produced  in 
the  size  of  the  thoracic  cavity  and  the  lungs  during  normal  res- 
l>iratioii  or  in  disease,  are  easily  determined  by  noting  the  sounds 
which  are  protlueed  by  tapping  or  percussing  w  ith  the  fingi-rs  the 


TIIK   MECHANISM  Ot    BREATIHNO. 


213 


tlioracic  walls  duriiiK  inspiration  an.l  expiration.    A  lo\v-i>itc-l>".l 
n-sona»it  sound  is  elicited  over  the  lunRS  eontainu.K  air.  whereas 
a  hijrh-i)itehed  non-vosonant  or  tynipanitie  liollow  sound  is  heard 
over  the  soli.l  viscera  an.l  ahdoininal  orjians.     Tn  .lis..as..s  where 
,.|,anjies  take  place  in  tlie  substance  of  tlie  liinjjs,  as  in  tubercu- 
losis  pneumonia,  etc..  alterations  occur  in  the  tone  .•lieited  on 
percussion.     These  alterations  are  ..f  jjreat  dia-nost.e   miport- 
anee     In  pleurisv,  a  condition  in  whicli  the  pleural  surlaces  are 
roughened,  a  friction  rub  or  vibration.  i)roduced  by  tlie  rubbiiiK 
of  tlie  roughened  surfaces  of  the  pleura  of  the  lungs  on  that  o 
tlu-  thorax  can  be  detected  by  placing  the  hand  over  tlu-  atTt'ctcil 
a.va     The  pain  following  a  broken  rib  is  caused  by  the  irritation 
of  the  pleural  membrane  by  the  broken  edge  of  the  rib.    It  is  al- 
leviated bv  making  the  ribs  immovable  by  tightly  strapi-mg  the 
thorax  with  adhesive  plaster  over  the  region  of  the  pain. 

Ri-si'iRVTOPY  SoiNn?.— Accompanying  inspiration  a  rustling 
sound  described  as  a  vesicular  sound  may  be  liear.l  over  most  of 
the  lung  area.  It  is  produced  by  the  dilatation  of  the  alve..li  and 
H„,  i,,„„chi.  Over  the  larger  air  ;.as.sag.'s  a  high,  sharper  tone 
is  heard  called  the  bronchial  breath  sound.  In  diseases  in  which 
the  alveoli  are  de-stroyed  and  the  lung  fills  ui)  with  Huid.  etc.. 
tlu-  bronchial  breath  sounds  replace  the  vesicular  sounds^ 

Effect  of  Respiration  on  the  Movement  of  the  Blood  and  on 
Blood   Pressure.— Within   the   thorax  the  changes  in  pressure 
accompanying  each  respiration  affect  the  heart  and  s.   influence 
somewhat  the  Miovement  of  the  blood.     In  thin  individuals  it  is 
..asv  to  confirm  this  by  observing  the  cfTect  of  breathing  on  the 
blood  flow  through  the  jugular  vein.     At  each  nisi.irat.on  the 
jugular  vein  is  seen  to  empty,  and  during  expiration  to  fill,     it 
simultam-ous  records  air  taken  of  the  blood  pressure  and  re- 
spiratory movements  in  or.liiiary  breathing,  it  will  generally  be 
observed  that  during  inspiration  there  is  a  rise  of  blood  pressure 
and  during  expiration  a  rail.    This  phenomenon  is  explained  as 
follows:     During    inspiration    the  heart  is  better  supplied  with 
b'ood  an.l  can  fill  more  .|uiekly  an.l  perf.-ctly  than  .luring  .-x- 
piration.  becaus.-  the  .lecrease  in  the  {.ressure  in  the  thora.x  at 
this  period  serves  to  accelerate  the  movement  of  venous  blood 


II 


214 


PHYSIOUXIV  FOB  DENTAL  STrDENTS. 


I: 


I 


into  the  tliorax  by  .'xpanding  tlio  larjrtT  veins.  The  .'xpaiision 
of  tile  luiiffs  at  inspiration  also  dilates  the  eapillaries  and  arteri- 
oles inibed.led  in  tiiese  tissues,  henee  a  greater  volume  of  l.Ioo<l 
ean  pass  through  them  in  the  same  unit  of  time.  If  the  heart 
beat  remains  eonstant  in  strength  and  rat»>,  the  increased  amount 
of  blood  pumped  during  insj)iration  will  cause  the  blood  pres- 
sure to  rise. 

It  is  well  to  bear  in  niiiul  that  imder  abnormal  conditions  the 
respiration  may  alfect  the  blood  i)ressure  to  a  dangerous  extent. 
For  instance,  in  the  attempt  to  force  air  from  the  lungs  under 
pressure  into  a  vessel,  as  in  blowing  up  a  football  or  testing  the 
strength  of  exj)iration  on  a  machine  made  for  the  purpos«\  the 
air  pressure  can  be  increased  within  the  thorax  to  more  than 
e(|ual  the  pressure  in  the  vessels  of  the  lungs,  and  the  circulation 
is  temporarily  .stopped  in  the  pulmonary  ves.sels.  The  blood  be- 
comes dammed  up  in  the  venous  system  and  forceil  out  of  the 
lungs  by  the  pressure  of  air.  This  experiment  is  dangerous  in 
one  who  has  not  a  first-class  heart  and  vascular  system.  The  ef- 
fects on  the  lungs  and  blood  pre.ssun>  of  sucking,  inspiration  and 
♦■xpiration  can  be  conveniently  reproduced  on  an  artificial  schema 
whicli  represents  the  thoracic  cavity,  lungs,  heart  and  related 
vessels,  as  shown  in  Fig.  .'51. 

Variations  occur  in  the  respiratory  movements  under  various 
emotional  and  physical  conditions.     Any  foreign  or  irritating 
boily  within  the  air  i)assages  will  cause  a  coiif/h.     This  consists 
in  a  forced  expiration,  during  the  first  portion  of  which  the  glot- 
tis is  closed.    The  irritating  substance  is  likely  to  be  expelled  bv 
the  sudden  oj)ening  of  the  glottis.     The  presence  of  irritating 
sulwtances  in  the  nasal  cavity  gives  rise  to  sneezing,  a  sudden 
and  noisy  expiration  through  the  nasal  passages  preceded  by  a 
i-ai)id  and  deep  inspiration.    In  cri/ing,  inspirations  are  short  and 
spasmodic,  followed  l)y  prolonged  expirations,  whereas  laughing 
IS  ijuite  the  n-verse.     Yawning,  the  expression  of  drowsiness  or 
ennui,  consists  in  long  deep  inspirations  followed  by  a  .short  ex- 
piration.    Jliccoitghiny  is  due  to  spasmodic  contractions  of  the 
diaphragm,  the  peculiar  sound  being  due  to  sudden  closure  of 
the  glollis. 


AHTII-'IllAI.  HKSl'lUATloN. 


215 


Artificial  Respiration.— In  ciis.'H  of  siisp.nil.'il  iM'spiraiimi  in 
human  li.-iiifrs  caiis.'.!  hy  <ln»vvnin;.'  .-xc-ss  i»f  aiia-stlifsia.  (ir  otli.T 

injury,  artificial  n-spiralion  is  oftn.  n ssary  Id  n-slorc  iiornial 

hreathinK.  Tlif  most  ctlici.'iit  of  tlicsi-  m.'ttio.U  is  ilcscriix-il  Ity 
Schaf.'r.  ami  is  known  as  Scliiifcr's  m.-tlwxl  (  Ki^.  :»-»■  '•«■  .If- 
scribes  tlif  m.-thod  as  follows:  it  consists  of  laying  tin-  subject 
in  the  prone  posture,  i>ref.'ral)ly  on  the  jrrouml.  with  a  thick 
folded  garment  underneath  the  chest  and  ei)i^'astrium.  The 
operator  puts  himself  athwart  or  at  the  side  of  the  subject,  facinir 


ViK.     32. — I'oHition     to     1>*'     inlniit.Ml     for 
(Schiifer.) 


i'fr.<tinK     MitiHciiil      usiiiiiition. 


his  head  (Fi^.  :i2)  and  places  his  hands  on  each  side  over  the 
lower  part  of  the  back  (lower  ribs).  He  then  slowly  throws  th,- 
weight  of  his  body  forward  to  Ix'ar  upon  his  own  arms,  and  thus 
presses  upon  the  thorax  of  the  subject  and  forces  the  air  out  of 
the  luntrs.  This  being  ctTected.  he  gradually  relax.-s  the  pressure 
by  bringing  his  own  bo<ly  u|)  again  to  a  nu)re  erect  position,  but 
without  moving  his  hands.  These  nunenients  are  rcp.'ated  reg- 
ularly at  a  rate  of  twelve  to  fifteen  per  minute  uutil  iu)rmal  res- 
l)iration  begins. 

Volumes  of  Air  Respired.— At  each  iuspirati<.n  the  lungs  lake 
in  about  .'.00  c  c.  of  air.  which  is  given  out  again  at  expiration. 
This  is  known  as  the  luhl  air.  After  the  completion  of  the  ordi- 
nary insi.iration.  it  is  i)ossible  by  a  lorced  inspiration  to  take 


2  If. 


rilYSIOI,(MJY    K(»H    DK.NTAt,    STI  l>K\TS. 


MOO  c.  c.  more  air  into  tlic  lungs.  This  amount  is  known  as  tlir 
i<nHi>l,  mrnlal  nir.  Lik.'wisc  aft.T  a  normal  expiration  al»out  i:>()0 
C-.  c.  more  air  can  he  .•xp.'ll..,!  from  thf  lungs.  This  is  known  as 
fh.'  supphmnilal  air.  In  spit.-  of  forcfd  expiration  tli.  iv  will 
still  remain  within  the  lungs  a'oout  2000  e.  e.  of  air  whieh  fills  the 
alveoli  and  air  tul).-s.  known  as  the  nxutml  air.  This  air  remains 
in  the  air  spaees  after  the  fore.-d  expiration  heeause  tlu'  lungs 
eannot  relax  to  their  fullest  extent,  l.eing  held  open  by  the  suc- 
tion prcHNure  of  the  thorax.  In  other  wor.ls.  the  thoracic  cuvity 
is  larger  in  the  expiratory  |Mtsition  hy  2000  c.  e.  than  the  lungs 
are.  That  this  is  the  ca.se  is  shown  hy  the  immediate  contraction 
of  the  lungs  into  a  small  volume  when  the  thorax  is  opened,  for 
then  the  atmosjiheric  pivssure  comes  to  he  equali/ed  on  the  out- 
side an<l  inside  of  th<'  lungs,  and  the  elastic  tissm-  emitracts  and 
forces  out  the  residual  air.  Fn»ni  this  it  is  obvious  that  the  elas- 
tic recoil  of  the  stretched  lungs  mu.st  always  tend  to  j)ull  the 
organ  away  from  the  chest  wall  and  thus  create  a  negative  or  suc- 
tion j.ressure  within  the  thoracic  cavity.  Anything  whieh  de- 
stroys this  relation  makes  br.'athing  impossd.le.  b.-cause  the  lungs 
are  no  longer  held  against  th..  chest  walls,  it  is  for  this  reason 
that  w„unds  in  the  chest  are  wiy  dangerou.s. 

The  trachea,  bronchi,  etc.,  rerpiire  (piite  a  little  air  to  fill  them, 
si,  that  only  a  part  of  the  tidal  air  reaches  the  alveoli.  In  other 
words,  it  is  only  a  jjortion  of  the  air  we  expire  that  has  really 
been  in  contact  with  the  res[)iratory  epithelium  and  has  sutfereil 
any  change  in  composition.  It  is  estinmted  that  about  140  c.  c. 
rei)rcsents  the  actual  volume  of  the  air  tubes. 

This  leaves  860  c.  c.  of  air  which  reaches  the  alveoli.  This 
amount  is  used  to  dilute  the  2000  c.  c.  of  residual  air  and  IT.OO 
c.  e.  of  .sui)plemcntal  air  already  in  th<'  alveoli.  In  fact  the 
functicm  of  breathing  may  be  .said  to  consist  in  continually  dilut- 
ing the  alveolar  air  with  a  (|uantity  of  fresh  air  in  order  that  its 
comi)osition  may  remain  more  or  less  constant. 

The  al)ove  analysis  shows  that  there  is  a  marked  ditrerence  be- 
tween the  inspired  and  the  expired  air.  It  shows  us  further  that 
of  the  oxygen  taken  up  by  the  bh.od.  only  j.art  appears  airain 
combined  with  carbon  in  the  gas  CO..    The  retention  of  ox\"gen 


UAt(K<M  S   KXt'llAM'.K    IN    I.INtiS. 


is  <lii('  to  tlif  oxidation  of  sulistmici's  wliit-li  do  i.ot  appcir  in  the 
.•xi>irfd  jrascs.  This  suh.jtrt  is  t'lili.v  d<'sri-ii»,d  iiiidiT  tlir  li.';id  ol' 
nsiiiniliirii  niinlitul  in  the  ciiaptci-  on  nwtat)olisin   *  p-  '*1'- 

Tlii'Hc  observations  do  not  .'nalilc  ns  to  dtcide  wii.tlirr  liif  laws 
of  diffusion  of  jrascs  apply  to  tlif  jrasi-ous  cxclianp'  of  tin-  lnn>,'s. 
To  do  tills  w.'  must  know  tlif  actual  pnssun's  (d'  tlif  nspiiatorv 
>.'HSfs  in  tlif  vfiions  MimxI  i-oiiiiiur  to  tlif  luiitfs  and  in  tlif  air  of 
the  alvfoli.  Many  typ.'s  of  f  xpf  .iiiifnts  liavf  hfi-n  df  \  isfd  to  ,ili 
tain  tlifsf  vahifs.  and  altlioimli  the  actual  tii.'iii-fs  vary  soiiu'wliat 
ill  the  hands  of  ditVfrfiit  investigators,  the  results  :is  a  wliolf  in 
.licate  that  the  khwous  fXt-hantre  of  thf  luiijis  is  dei'cnd /nt  solely 
on  thf  prfSfiice  of  a  hijjlifi'  iiressure  of  oxyjreii  and  a  lower  pr.s- 
sure  of  carbon  dioxide  in  the  alveolar  air  tlian  are  pivs.'iit  in  the 
blood  coniiiiK  to  the  Iumks.    Tln'  ability  of  ha-iii.>nlobiii  to  take  up 

oyy^reii  with  Kn-at   rfadiiicss  at  oxytreii  pressures  which  ex .1 

■")()  or  (iO  iiiiii.  mercury  pressure  indicates  that  Uie  blood  can  Mill 
obtain  oxygen  from  air  which  contains  only  oiielialf  of  the  nor- 
mal pressure  (d"  oxy-rcii.  In  whatever  way  we  estimate  it.  the 
oxytren  |)ressui-e  in  the  alveoli  is  always  -greater  than  this. 

\Ve  will  not  fio  into  details  i-e<;ardin^r  the  iiietliods  whicli  have 
lu'cn  eiii|iloyed  in  solution  id'  these  jirobleiiis;  suflice  it  to  say  that 
a  very  fair  sain|)le  of  alveolar  air  can  be  secun-d  by  collectiii«  a 
sami»le  of  air  from  a  tube  throu<,'li  which  a  forcfd  expiration  has 
))een  made.  The  last  portions  of  such  expired  air  must  obviously 
be  .     eolar  air. 

Mechanism  of  Gaseous  Exchange  in  Lungs.— We  have  seen 
that  ill  the  blood  thi"  pressure  or  ti'iision  of  the  oxygen  is  <jreater. 
\vliei>'as  that  «*"  the  CO.,  is  less  than  in  the  tissues.  Tiiese  rela- 
tions will  a( ,  .(Unt  for  the  sjas  excliaii<re  which  occurs  between  the 
blootl  and  tissues  if  we  apply  the  physical  law  of  tin-  ditfusioii  of 
frascs,  which  states  that  two  ;;ases  under  ditVereiit  pressures  and 
separated  by  a  membrane  tliroutrh  which  they  may  jiass  fine- 
ly, will  mix  with  facli  other  until  the  tensions  on  both  sides 
of  the  membrane  are  e<|ual.  Uefore  this  law  can  be  applied  to 
fxplaiii  the  excbaii'ie  of  «ras<'s  between  the  blood  and  air  within 
the  lunjrs,  we  must  prove  that  tie  tension  of  the  oxyjjen  is  less, 
and  of  the  CO.  greater  in  the  venous  blood  than  in  the  alveolar 


218 


i'llV.S|nl,(MiV    FOI{    DKNTAli   nTIDKNTS. 


air.     A  coiiNiihrntioii  of  tlii'Mt-  problt'iiiH  In  iiicliKli-d  iiiiili-r  tlic 
siil».it'«'t  of  i.rhnnil  n Kpinilioti. 

Th»'  ihH[)in'(l  or  »itiiioM|»h<'ric  air  is  ii  inixturi'  of  ox.Vtfcn,  cur- 
hon  tlioxi(i<>  ami  nifrojrcii,  ami  is  n'lativciy  coiiHtant  iimli-r  onli- 
nary  comlitioiis.  The  cxpiri'd  air  varies  Hoim-wliat  accordiinr  to 
till'  nitt'  Hiiil  ficpth  of  respiration.  The  foIiowiii«  tahii'  jjivcs  the 
awrm^e  |>t'rcciitaKi'  coinposition  of  inspired  and  ex|)iretl  air: 

NitroKPii 

liiHplred  alp 7!t 

Kxpired  air  7y  + 


Oxynen 

<"() 

20.96 

1)  .(I 

16.02 

4.38 

("IIAl'TKU  XXIII. 

TIIK  HKSIMHATION   (((.ntdi. 

Nervous  Control  of  Respiration.— TtniiT  nonnal  rondiiions 
we  hrciitlii'  t'ntiii  14  to  1H  tiin.-s  a  iiiiimtc.    AcconliiiK  to  the  do- 
inaiKJ  of  tlif  tissins  for  o.xyKiii.  we  Itn-atlif  fast  or  slow,  but  the 
ri'spiratioiis  an-  rlivllimic  in  tiiiH    and  luiti.-r  lik.-  conditioiiH  arc 
i>i|iial  in  volume.     Tlic  respiratory   inovenn'nts,  unlike  thow  of 
the   heart,   are   entirely   dependent    upon    iiuixilses   transmitted 
from  the  central  nervous  system.    These  come  from  the  so-ealled 
respiratory  centers  in  the  medulla  olilonjrata  (  p.  2.")«i).    Anatomic- 
ally these  centers  cannot  he  sharply  l(M-ali/ed.  hut  destruction  of 
the  portion  of  the  medulla  in  which  they  exist  causes  an  imme- 
diate cessation  of  respiratory  movements.     The  centers  are  con- 
necteil  with  the  muscles  of  res|)iration.  by  the  phrenic  nerves— 
to  the  diaphragm.— the  intercostal  nerves— to  the  nmsclcs  of  the 
,.il,s, — and  by  the  nerves  running  to  the  larynx  and  nares.     Liki' 
all  other  nerve  centers,  the  respiratory  center  is  influenced  by  af- 
ferent impuls«'s.  the  chief  ones  of  which  come  from  the  lun^t^i  by 
way  of  the  vapus.  but  there  are  many  others.     In  fact  all  the  sen- 
sory U'Tves  of  the  body,  as  well  as  the  hijjher  centers  of  the  brain. 
a»-    able  to  influence  the  respiratory  center.  Disease  of  the  phren- 
ic nerves  causes  paralysis  of  the  diai)hraKm.  and  impairs  the  ven- 
tilation of  the  lunjrs.     Likewise  ])aralysis  involving  the  s|)inal 
cord  below  the  exit  of  the  phrenic  nerves  may  i)aralyzt"  tin;  nerves 
of  the  thoracic  nniscles.  and  throw  the  whole  work  of  respiration 
on  the  diaphrasjm. 

If  the  vajrus  nerves  of  a  dog  or  eat  are  cut  in  the  neck,  the 
respiration  becomes  deejier  and  slower,  yet  the  volume  of  air  re- 
si)ired  per  minute  is  not  -rreatly  altered.  This  chan«re  is  due  to 
tlu'  elimination  of  stinudi  normally  cominir  from  the  lunps  by 
way  of  the  va^i  to  the  respiratory  center,  which  serve  to  control 
the  depth  of  respiration.     It  can  be  experimentally  demonstrated 

219 


■grwiiML  ~«fef^ 


fS^ 


:  tc-  ^  mJi^JiiJtll^Mm  " 


220 


I'nYSI()I,(MiY    FOR    DENTAFi   .STl'DENTS. 


tliat  the  colliipsc  of  flic  Jilvcoli  of  tlic  hiiifis  wliicli  occurs  iit  the 
cud  of  iiorinal  cxpii'atioii.  and  the  strctdiiiip  of  the  ahcolar  walls 
wliicli  ocelli's  at  the  end  of  noriiial  inspiration,  cause  stimuli  to  he 
passed  aloiifj  the  vajri  to  the  center,  and  tliat  these  stimuli  l)rinjij 
on  the  next  jtliase  of  respiration.  The  hreakiiig  of  the  connection 
hetweeii  the  lunjis  and  the  alveoli  destroys  this  influence  and  the 
respirations  liecome  deep  and  slow. 

In  the  ahsence  of  the  vagi,  the  hifjrher  centers  assume  ])artial 
control  of  the  rejjulation  of  the  respiratory  moveiiieiits.  If  they 
also  ar(;  destroyed,  however,  hi'eatliiii};  becomes  inadeijiiate  to 
maintain  life,  altlioujrh  the  center  itself  is  still  able  to  keep  up  a 
modified,  rhythmic  respiration. 

Hhfi.kx  Resi'IKATory  MdVKMKNTs. — The  cutaneous  nerves,  es- 
jK'ciall.v  those  of  the  face  and  abdomen,  have  a  marked  intlueiice 
on  resjjiration.  These  can  be  excited  by  heat  or  cold  or  pain ; 
for  instance,  a  cold  bath  will  cause  a  deepenin<;  or  quiekeniiifr  of 
tiie  I'cspiration.  An  example  is  found  in  the  forced  expiratory 
etfort  made  on  inhalation  of  acid  or  sharp  snielliii<j  substances, 
which  not  only  atfect  the  olfactory  nerves,  but  al.so  the  sensitive 
endinsrs  of  the  tifth  nerve  in  the  nasal  mucous  iiiembrane. 

Chemical  Control  of  Respiration. — In  spite  of  this  very  etfec- 
tive  method  of  nervous  control  of  the  respiration,  there  is  an- 
other no  h'.ss  iiri])ortant  means  of  res|)iratory  control,  which  de- 
pends on  the  ability  of  chemical  substances  in  the  blood  to  stim- 
ulate the  respiratory  center.  The  su])stances  which  most  readily 
affect  the  center  are  acids,  such  as  carbon  dioxide  (which  in  solu- 
tion forms  a  weak  acid.)  and  lactic  acid,  which  is  formed  under 
certain  conditions  in  the  body.  Lack  of  oxyf^eii.  if  it  be  consid- 
erable, also  causes  tlie  center  to  show  marked  sijins  of  activity. 
In  till'  introdu(t(>r\-  cliapter  the  physico  chemical  projierties  of 
the  blooil  and  tissue  tluid:i  were  discussed.  It  will  be  recalled 
that  these  are  practically  neutral  fluids,  that  is.  they  show  an  al- 
most exact  balance  in  the  number  of  hydrofren  and  hydroxyl 
ions,  a  condition  wliieii  determines  the  neutrality  of  a  fluid.  Any 
increasi'  in  the  amount  of  carbon  dioxide  in  the  blood  would  form 
proportionately  more  carbonic  acid,  \\iiicli  yields  hydrogen  ions, 
and  thus  tend  to  destroy  the  neutral  balance  of  the  blood.    This 


Ij 


CIir.MKAI.    (•(•NTHDl,    OK    |{1>1'IH ATldX. 


221 


f 

{  s 


increase  in  the  liydrofren  ion  eoneeiitration  in  tlie  l.loo.l  is  sutli- 
eient  to  stiniwli.te  the  respinitor.v  eent.T  an.l  iniy;nient  th.'  rMv 
ir,(l  (leptii  of  respiration  in  order  to  expel  the  earlx.n  .lioxhie 
an.l  thns  r.Mluee  the  aei.iity  of  the  hioo.l.     All  aei.ls  whieli  vi.l.l 
hv.lro^en  ions  in  solution  have  tins  etV.'et  on  r.'spiration  when 
tiiev  are  in.jeete.l  into  the  hioo.l.     La.-tie  aei.l.  whi.-h  is  forni.'.l 
whi'n  the  oxy^."n  supply  to  the  tissu.-s  is  .lin.inishe.l  ..r  ina.le- 
•  luate.  is  perhai)S  th.'  in.«st  important  laetor  eoininj:  int.)  i.hiy  in 
th.'  stimulation  of  the  r.'spiratory  eent.M'    whi.-h    o.-eurs  .luriiu; 
exereise.     The  earhon  ilioxi.U'  tension  of  tin-  l.io.ul  .lurini:  ex.r- 
cis.'  mav  h.-  actually  .leer.-ased  .nvin-j:  to  the  inerease.l  v.'ntilati.m 
of  th.-  lunjrs  as  a  result  of  the  present  of  laetie  aei.l  in  tli.-  hioo.l. 
Th."  increase  in  breathiuf;  .lu.-  to  lack  of  oxyjren  is  not  nearly 
so  easilv  .-lioitea  as  that  caused  by  .'x.vss  of  acids.     In  fact,  th.' 
l>erc.'nta<,'e  of  oxy-r.-n  may  h.'  .liminish.'.l  t.)  ahout   on. '-half  of 
that  fonn.l  in  the  atnmspii.MV  before  bn-athin-  is  marU.-.ily  af- 

f.'cted. 

In  disturbances  of  the  ^'ase.uis  ex.-haufre  of  the  luufrs.  th.'  r.'- 
spiratorv  center  attempts  to  compensate  for  the  chan^'e  by  in- 
cr.'asinjr  the  number  an.l  th.-  .l.'ptli  of  th.'  respirations.  If  th.' 
Has  .'xchange  be  markedly  insutiHcient.  th.'  bn'athing  b.'c.)m.'S 
v.'rv  nmch  exa-fierated.  and  practically  all  possible  r.-spirat.iry 
muscles  ar.'  call.-d  into  play.  This  is  the  .-ase  .lurin-  an  atta.-k 
of  asthma,  in  which  the  muscles  of  the  arms  an.l  ab.lom.'U  ar.' 
used  bv  the  pati.'ut  in  his  .'tforts  to  .)l)tain  .'uoujih  air.  Ditli.-nlt 
br.>athinK  of  this  kin.l  is  known  as  (hisptxnt.  If  th."  jras  ex.-han-r.' 
is  very  insuflicient.  the  phenomenon  of  osphiijio  sets  m. 

The  eontn.l  of  th."  r.-spiration.  th."r.'l'.)r.".  may  be  sai.l  t.)  b."  a 
double  one.  one  .h'l.en.lent  .m  th."  n.'rv.'  supply  of  the  r.'si>ira- 
torv  center  from  the  atferent  seiisoi'y  an.l  eer.'bral  n.'rvs,  an.l  th.' 
other  on  the  chemical  constitution  of  th.'  I.Io.mI.  whi.-h  stimnlat.'s 
the  center  directly.  Hoth  play  an  im|)ortant  part  in  tlu-  .-ontrol 
of  the  respiratory  mov.'ments. 

The  hroinhiol  nuischs  are  su|.pli.'<l  tlirout;h  th."  va-i  wilh 
nerve  fibers  which  i)ro.luc.'  dilatati.>n  an.l  const ricti.m  ..f  tii.' 
broiu'hi.  ,Iust  what  the  normal  con.litions  are  whi.-h  call  for  th.' 
action  of  these  nerves  is  not  known.    It  is  generally  thought  thai 


223 


I'HYSl(>I,(MiY    FOR    DFATAI,    sTIUKNTS. 


Hstliniji  is  cauHcil  by  the  coiistrictioii  of  the  broiidiiolcs  by  spasm 
of  till"  bronchial  imisclcs.  Atropiii.  a  dnif,'  which  jiaralyzcs  cer- 
tain nerves  is  of  therapeutic  use  in  this  disease,  since  it  jiaralyzes 
the  nerve  endings  in  the  bronchial  muscles.  Adrenalin  is  also 
sometimes  of  use. 

The  Effect  of  Changes  in  the  Respired  Air  on  the  Respiration. 
A  very  slight  increa.se  in  the  percentage  of  carbon  dio.xide  in  the 
(ih'(ohtr  air  is  accompanied  by  a  vei'v  marked  (|uickening  of  re- 
spiration. On  the  other  hand,  the  carbon  dioxide  pont<'nt  of  the 
(it)iiospknr  nuiy  be  increased  to  ii. DUt  one  per  cent  without  em- 
barrassing the  respiratory  function,  except  during  muscular 
work,  and  it  is  only  at  concentrations  of  carl)on  dioxide  of  three 
or  four  per  cent  of  an  atniosi)here  that  the  resj)iratory  function 
is  seriously  excited.  The  rea.son  for  this  is  that  the  inspired 
air  becomes  greatly  diluted  before  it  reaches  the  alveoli,  so  that 
n  slight  increase — up  to  one  per  cent  of  carbon  dio.xide — in  the 
atmosphere  only  (luickeiis  and  <ieepens  the  respiration  suificieiit- 
ly  to  maintain  the  pres.sure  of  carbon  dioxici.'  at  its  normal  level 
in  the  alveoli. 

An  increase  in  the  o.xygeii  i)ressure  has  no  such  etfect.  In  fact 
pure  o.xygen  has  scarcely  any  influence  on  the  rate  of  breathing 
in  the  normal  man.  In  persons,  suffering  with  heart  failure  or 
diseases  in  which  the  respiratory  function  of  the  lungs  is  im- 
paired, however,  the  presence  of  a  high  concentration  of  oxygen 
in  the  alveoli  may  make  it  pos-sible  for  the  oxygeii-starv  -l  blood 
to  obtain  enough  of  this  gas  to  .saturte  it  and  thus  improve  the 
general  condition.  The  reason  for  these  effects  of  oxygen  is  that 
under  normal  conditions  the  i)ressure  of  oxygen  in  the  atmos- 
Iihere  is  more  than  sufficient  to  saturate  the  liaMiioglobin  of  the 
blood,  so  that  an  increase  in  the  oxygen  i)ressure  will  add  only  a 
small  amount  more  of  o.xygen  to  that  dissolved  in  the  |)lasma  al- 
ready. On  the  other  hand,  tiie  oxygen  pressure  in  the  atmos- 
lihere  may  Ik-  reduced  to  less  than  half  that  found  at  sea  level 
without  destroying  life.  This  brings  up  the  interesting  (luestion 
of  mountain  sickne».s. 

MoiNTAiN  Sickness.— At  an  altitude  of  ."),000  metres  (about 
16,000  feet)   the  air  is  reduced  to  a  little  over  half  an  atiiios- 


VF.NTII.ATKIN. 


•J'_':5 


l)li('r(\  and  tlif  oxyjrt'ii  Ifiision  is  therefore  only  about  eleven  per 
cent  of  iin  ntniosi)liere  in  i)laee  of  twenty  per  eent.     Therelore. 
in  order  to  ,sn|>ply  the  \m-iU-i\  oxygen,  respiration  must  heeoine 
more  rapid.     This,  however,  hy  washing  out  the  earhon  dioxide, 
serves  to  reduee  the  tension  of  earhon  dioxide  in  the  alveoli  and 
blood  to  syeh  an  extent  that  the  aetion  of  this  (jas  on  the  n- 
spiratory  center  is  weakened,  and  breathing;  may  be  very  slow 
or  cease  for  a  time.  i)rodneinji  a  condition  known  as  aitnea.    Tiie 
lack  of  oxyjien  weakens  the  heart,  the  sli-;htest  muscular  move- 
ments are  accomi)lished  with  ditlHculty.  and  the  individual  suf- 
fers from  nausea.  v  headache  and  general  weakness.  After 
livinjj  for  some  t'l         '      leh  altitudes  a  person  becomes  accus- 
tomed to  the  rarit.>     ,•   The  atmos])here  and  in  some  maimer  is 
able  to  compensate  for  the  lessened  oxygen  in  the  air. 

Vkntii.ation. — The  ilisafrreeable  0(h)r  of  a  crowch'd  room  and 
the  symptoms  which  accompany  it  are  well  known  and  are  usual- 
ly attributed  to  tlie  rebreathing  of  air.     In  support  of  this  the 
historical  incident  of  the  lilack  Hole  of  Calcutta,  in  which  many 
jteo|)le  jierished  from  lack  of  air.  is  often  citeil.    We  liave  already 
seen  that  atmospheres  up  to  one  per  cent  of  carbon  dioxide,  or 
containing  less  than  half  of  the  normal  j)ercentage  of  oxysreii. 
can  be  respired  with  no  ill  etfects.     lUit  tin-  i)ercentaKe  of  carbon 
dioxide  in  the  worst  ventilated  room  does  not.  as  a  rule,  rise  above 
five-tenths  per  cent,  or  at  most  over  one  per  cent,  of  an  atmns- 
])here.     That  this  amou!it  atfects  our  btnly  metabolism  is  imi)os- 
sible.  since  the  carbon  dioxi<le  in  tlu'  alveolar  air  is  kept  at  a 
constant  level  of  from  five  to  .six  per  cent  by  the  control  which  the 
respiratory    center    exercises    on    the    respiratoiy    movements. 
Moreover  perfectly  normal  respiration  can  take  place  in  a  room 
where  the  oxyjien  content  is  so  low  that  a  match  will  not  burn. 
Because  of  these  facts  it  was  sufrpested  at  one  time  that  a  toxic 
substance  might  be  present  in  the  ex|)ired  air,  but  this  has  not 
been  confirmed  hy  suhse(|uent  investiKators.  in  spite  of  the  fact 
that  tliere  is  a  nornud  percentage  of  oxygen  and  carbon  dioxide,  a 
room  may  be  unbearably  close  if  it  is  too  warm  and  the  air  is 
saturated  with  moisture.    So  long  as  the  body  can  radiate  its  heat 
ipiickly  into  the  atmosphere,  the  room  does  not  feci  .stuffy,  but 


M 


"  ! 


.1  -H 


:|i 


if 


--■*  IMIVSI(H,(i(iv    FOK    DKNTAI,    STIDKNTS. 

wluMi  .•viij,nri.Ii..ii  is  slow,  b.-causc  (.f  si.tun.tion  of  the  air   an.I 
lu-at  IS  no  lo.,f.,.r  ^iv....  off  ,|uicl<ly  l.y  fh,.  bo.ly.  tlu-  in.livi.iuals 
111  th..  i-oo,n  iMTon.,-  very  uiiconifortahl...    An  I'lcctric  fan   which 
.listr.l.ut,.s  th.-  air  .-v.-nly  ov.-r  the  roon,  an.l  thus  .,uic-k..ns  tho 
ivinoval   ol    the  warni   moist   air  imn.e.liately  surround inj,'  th,. 
l'o.iy.  a.hls  much  to  the  comfort  of  the  person.  While  it  is  not  wise 
to  (liscoura-e  fresh  air  in  public  offices  ami  j.rivate  houses,  it  is 
absolutely  nec-ssary  that   the  ventilating  enfrineer  should   pav 
hml  to  somethiHK  Ix'sides  the  j.erceutajr,.  of  oxygen  and  carbon 
'iiox.de  in  the  room.     He  shoul.l  also  direct  his  etforts  t.)war.ls 
.•ooling  an.l  incn-asing  tlu-  circulatio..  of  the  air  that  .surroun.ls 
the  bodi.-s  of  th.-  in.lividual.s,  by  s,-ttit,g  the  air  in  motion  bv 
means  of  fans. 

The  con.litions  of  tem|)erature,  the  moisture,  an.l  th.-  win.ll.-.ss 
i"trii..sph.-re  tou.i.l  in  publi.-  rooms  an.l  hom.-s  .limiuish  th.-  h.-at 
loss  ot  th,-  l)...ly  an.l  thus  the  h,-at  iu-,.,lu.-tioM.  which  m.-ans  that 
th,-  activity  of  th.-  cocupants  must  b,-  l.-ss.  A  r.-as.uiable  tem- 
perature with  a  r,-lativ,-ly  low  ju-rc-ntag,-  of  moistur.-.  an.l  or.li- 
nary  care  m  provi.ling  fr.-sh  air.  will  maintain  th.-  prop,-r  hv- 
git-nic  conditions  of  a  room. 

The  Voice. 

Th,.  voice-pro.luoing  moclianism  in  man  consists  of  th,-  trachea 
through  which  the  air  is  blown  from  th.-  lungs:  th.-  larvnx   the 
>"o.lih.-,l  upp.-r  portion  of  th.-  trach,-a.  whi.-h  contains  tlie  vocal 
••onls;  an.l  th.-  j.harynx.  an.l  uj.p,-r  air  i.a.ssag.-s.     Th,-  larvnx 
forms  th,-  .-ntran..,-  iuto  tlu-  trael,..a.    It  is  compos.-.l  of  a  numb,-r 
of  eartilagu.ous  plat,-s  which  are  unit.-.l  in  a  manner  to  form  a 
box.    Str.-tcli.-.i  from  front  to  back  on  .-a.-h  side  acrixss  th,-  upper 
portion  of  th,.  larynx  are  thin  sliarp-,-,lg.-,i  m.-mbraiL-s.  the  vocal 
cords.    The  attachments  of  the  muscl.-s  to  th.-  cartilages  and  th.- 
Jirticulations  of  th..  s..v.-ral  cartilag,.s  with  ea.-h  ..thei-;  an-  so  ar- 
ning,-,l  as  ,-ither  to  tighten  or  loo.s.-u  the  tension,  or  in,.r..ase  or 
•l.'crea.s..  th,"  op,.ning  betw,.,-!,  th,-  edges  of  the  cor.ls.     The  cleft 
b,.tw,M.n  th..  .-or.is  is  .-alL-.l  th.-  glottis.     The  length  of  the  vo.-ai 
<'or.ls  varn.s  fr.,m  11   to  l.'.  mm.,  being  l.H.ge-  in  m...,  than  in 
woni,-n  and  children.    ]Jranches  of  the  vagus  and  th,-  sjiinal  ac- 


Tin;  voicK. 


225 


ct'ssorv  ncm-s  supply  tlic  imiscl.'s  ..f  tlu"  larynx  with  im.tor 
nerves.  The  sensory  nerves,  arisinK  in  the  epithelium  of  the 
larynx,  are  also  l.ranehes  of  the  vajrus.  Meehanieal  stimulation 
of  the  mueous  memhrane  of  the  larynx  or  eleetrieal  stimulatu.n 
of  the  superior  larynK<'iil  U'-rve  will  cause  a  eoiij?h  or  a  toree.l 
expiratory  movement.  ,  n     j 

The  Changes  Which  Occur  in  the  Position  of  the  Vocal  Cords 
.iurinji  the  j)nuluetion  of  eertain  s(mn.ls  may  he  stu.lie.l  l.y  the 
ns.'  of  the  lar,,n!)osn>l>'.  the  prineii.h'  of  whieh  is  shown  in  Fi«. 
;!:j.  The  view  obtained  from  sueh  an  instrument  is  shown  in 
Fi.'s.  :i4  and  ;!•').    The  hase  ..f  tlu'  ton-rue  ai)pears  at  the  toj):  hc- 


'  depressor 


Pij;     :?s._ni;,f,iaiii    of   liiryiiKosooiw. 


low  this  is  the  e.l-..  of  the  epi-h.ttis.  the  flap  of  tissue  guanhnfi 
the  eiitranee  to  the  larynx,  and  below  in  tlio  middl.'  hiu'  an-  seen 
tlie  true  voeal  cords  as  white  shining'  membranes.  Just  above 
these,  on  both  sid>  s.  are  two  pink  flaps  of  tissu.-.  the  false  rocal 
cmh     These  secr-l"  a  fluid  which  moistens  the  true  cords. 

The  Production  of  the  Voice.~lf  the  vocal  cords  are  put  in 
i,  Stat.-  of  tension  ami  tin-  aperture  between  them  be  narrowed, 
eausing  them  to  ortVr  a  resistance  to  the-  j.assa-e  of  air  issuing 
from  the  lungs,  thev  may  l)e  made  to  vibrate  ami  to  pro.luce 
sounds.  It  has  been  exi..'rimeiitally  defrmiiied  that  a  pr.'ssure 
of  expired  air  of  from  140  to  240  mm.  of  water  is  rcpured  to 


»26 


rHYsloLiKiV    POK    OKNTAI,    nTIDKNTS. 


prodiuv  a  sound  of  th.-  onliiijiry  i)itcli  iiiid  loii.liii'ss.  while  in 
loud  shoutiiiK  niuch  •jri-t-iitci-  jji-cssui-cs  arc  necessary. 

The  sound  of  the  voice,  like  any  other  sound,  may  varv  in 
I»itcli.  loudness  an<l  (|uality.  The  rauKc  of  pitcli  of  the  voice  is 
Kt'iicraliy  alwut  two  octaves,  the  pitcli  itself  heing  determined 
primarily  hy  the  lengths  of  the  cords.  This  accounts  for  the 
hij,'h-j)itched  voice  of  children,  in  whom  tiie  cords  are  short,  and 
the  low  i)itcli  of  the  voice  in  m.'n.  in  whom  they  are  lonp.     In 


Kik'.  34, — I'oKitiiiii  ,if  111,.  Kldttis 
piiliininaiy  to  the  uttfiaiK  c  (if 
sound.  r.i,  tiui'  vocal  cord;  ,(r.  ;ir.v- 
tiTioid  CMitiluKc ;  /).  i,;iii  of  'In-  ipi- 
KlottiK.  (  Knini  ."^tiwiut's  I'h.vsi- 
oloK.v.) 


KiK.  35. — I'osilioh  of  op.ji  Rlottis. 
/.  toiiKuc:  f,  .-plKlotlis;  nc.  uty-,.(.i- 
HlolthlHHii  fold:  r.  cartiliiKP  of  Wiis- 
l"'iK  :  <ir.  iir.vtfiioid  ciiitilaKi- :  o, 
Klottis:  r,  v.-ntricli-  of  MoiK.iKiii  : 
li.  tnif  vocjil  loi-d  :  Is.  falsi-  vocal 
cord.       (  Ki-om   .Stewarts    I'hysioloK.v. ) 


suijfinj,'.  three  iVK'ist.-rs  can  he  <listin},niished.  the  head,  middle 
and  ehesf  re^'i.st.-rs.  The  .leej.er  notes  of  tlw  siufjer  come  from 
the  chest  register,  and  are  j)r,Hliice.l  hy  th..  vihrations  of  the  en- 
tire cords,  whereas  in  the  upji.-r  registers  only  the  inner  edge  of 
the  cords  vihrate. 

The  intensity  or  h„i(hu ss  of  a  vocal  .sound  depends  upon  the 
iiinplitu.h.  of  th,'  vihrations  of  the  vocal  cord.s.  and  this  is  j.ro- 
portional  to  the  strength  of  the  expiratory  hla.st.  The  pitch  of 
a  note  ri.ses  and  talis  somewhat  with  the  intensitv  of  the  ])ivs- 
sure  of  the  air,  and.  f,.r  this  iva.son  high  notes  are  usuallv  loud 
notes.  The  qnalitu  of  th.-  voice,  lik.'  tiiat  of  a  musical  instru- 
nient.  depends  on  the  overtones,  or  harmonics,  that  it  produces. 
For  example,  wh.-n  a  stretched  string  is  made  to  vihrate.  it  not 
only  vihrates  as  a  whole,  hut  portions  of  it  vihrates  independent- 
ly and  gives  off  sej)arate  tones  which  are  known  a.s  overtones. 


SI'KKCII. 


227 


Sine."  tlu>  toih-  which  the  string  imxlucrs  hy  thr  vihiiiti..M  ot  its 
..ntir."  h'ugth  is  th..  h)U.h-st  an.l  U.w.-st  in  pitch,  it  is  p.ckc.i  out 
as  the  fuiulamcntal  tone.  The  fun.la.nciital  tones  of  mstrn- 
,„,.nts  n.av  he  exactly  the  same,  hut  the  tones  yet  .liirer  from  one 
anotluT  liecause  of  the  numher  an.l  the  int.^nsity  of  tlie  over- 
tones. Tlie  .|uality  of  th.-  voice  .h-pen.is  m.  the  overtones  ,)ro- 
.luce.I  an.l  intensifi.-.l  in  th.'  piuirynx  an.l  upp.-r  air  .•hamh..rs. 

Speech. 

Th.-  pure,  nuisical  tones  pr<..lnc.Ml  hy  th.-  vocal  cor.ls  ar.-  m...ii- 
fi,.,l  hv  chanfr..s  in  tiu-  charact.-r  of  liu-  air  passaf?.-s  alu.v.-  tlu-m. 
The  various  comhinations  which  are  i)r.Hh"-.-.l  fiiv.-  ris.-  to  smin.is 
which  make  up  sp.-.-ch.  Many  of  the  simple  c.mihinations  are 
foun.l  iu  ail  lansuajics.  hut  .-very  languaj,'.-  is  charact.-riz.-.l  hy 
certain  sounds  which  are  p.-culiar  t(»  it. 

The  soun.ls  pro.luc.-d  in  speech  may  h.-  .livi.h-.l  into  two 
firoups.  the  vowels  an.l  th.-  c.)ns..nants.  Th.-  vow.-l  s.nui.ls  ar.- 
contiimous  and  arc  fonn.-d  in  th.-  low.-r  air  i.assa-.-s  with  tin- 
h.-lp  of  the  }rl.)ttis.  Th.-  consonants  an-  pro.lnc.-.l  hy  moiv  or 
l.-ss  compl.'t.-  interrui)tions  of  th.-  .nitdowiiifr  air  in  .litren-nt 
l)ortions  of  th.-  vocal  tract. 

All  the  vow.-ls  can  he  i)roduce(l  in  tli.-  whisp.-r.-.l  voic.-,  that  is. 
thev  can  he  pro.luced  with.mt  th.-  actual  vihration  of  th.-  vocal 
cords.  The  mouth  cavity,  how.-v.-r.  assumes  th.-  .saim-  position  in 
th.-  case  of  th.-  whisp.-r.-d  vowel  as  it  .lo.-s  f.)r  th.-  spok.-n  vowel. 
Hy  clianjiiiiff  th.-  shape  of  th.-  air  passages-  the  various  vow.-l 
tones  arc  pr.xliice.l.  In  Fijj.  :{6  an-  s.-eii  th.-  various  positions  of 
the  toi.gu.-  an.l  palat.-  f..r  th.-  pro.iuction  of  th.-  .litf.-n-nt  vow.-ls. 
When  v.)w,-ls  are  heiiii;  utt.-n-d,  th.-  s.)ft  palate  dos.-s  th.-  .-n- 
t ranee  to  the  nasal  cavity. 

The  consonants  an-  nam.-d  acconling  to  th.-  position  at  which 
th.-  interruption  of  the  air  <-urn-nt  tak.-s  place.  Th.-  lahials  an- 
formcd  at  the  lips:  p,  h;  tlu-  .l.-ntals.  h.-tw.-.n  the  toiiKiu-  an.l  th.- 
tccth:  t,  d.  The  {?utterals.  k,  K,  c.i.  aris.-  hctw.-.-n  th.-  post.-rmr 
portion  of  the  arclu-d  toufiue  an.l  tlu-  soft  palate:  an.l  th.-  (i.-r- 
maii  r  is  produced  with  the  help  of  vibrations  ol  the  uvula. 


w.cm 


228 


I'llVSIoriCHlY    FOR    DENTAIi    STt'DENTS. 


Sounds  like  in.  n.  i\g.  an-  tcrnit'd  nasal  consonants,  since  they 
Jirc  sounded  throusjli  the  nasal  cavity  (sec  Fi}?.  'M\). 


ViK.    H«. — The   iioHiti.in   i>(   tlir   tcinKiii'   ;mcl    lips  (liiiiiiK   the   ult.niiK.'  iif    llii' 
l>>ttiis    iiMliciit.'d. 


!^4 


(ilArTKK  XXIV. 
TIIK  Ki.rii)  EXCHl-noNS. 
The  Excretion  of  Urine. 
The  Composition  of  the  Urine.-Tl.o  wnst.-  sul.stan-y  nsuli 
i„.r  from  th.'  pnuTssrs  ..f  mrtaholism  in  th.-  tissurs  a.v  v\unmn\M 
iZm  th."  l.o(lv  in  a  Kasoous.  th.i.l.  or  solid  stat...     VV.th  llu-  .■x.-..,,- 
tion  of  tlu'  carbon  .lioxi.l.'  aiul  water  of  the  .■xpnv.l  air.  an. I  c'r- 
lain  substances  whicl.  arc  excreted  into  the  intestn.es  or  api.ear 
in  the  secretions  of  the  slvin  plands,  the  metabolic  i.ro.hn-ts  are 
eliminated  in  the  ui -le. 

Tin-  composition  ..f  the  urine  is  theretor..  rather  complex  an. 
varies  .'rcatlv  with  th.-  nature  ..f  the  foo.l  an.l  th..  amount  o 
water  tak.-n.'  i'.v  car.dul  amdysis  of  the  urin.-  from  a  nund.er  ot 
in.livi.luals  on  or.linary  di.-t,  the  avrajje  amount  of  the  various 
eonstituents  in  what  may  be  consi.h-r...l  a  norn.al  urn...  can    .e 
estimated.     Fresh  hun.an  urine  is  a  .-lear  >'f;;;,^.'';'/' J'''; 
heuvi.-r  than  water,  having  a  specific  gravity  of  l.OK.  to  l.U_      It 
tested  with  litnms  paper  it  usually  shows  an  a.-i.l  r..act.on.  wh.eli 
is  n.ainlv  due  to  th..  pres..nci.  of  aci.l  salts,  such  as  so.hum  dd.y- 
drogon  i,h..sphates.  but  partly  also  to  acid  substances  .l.-nv...! 
from  proteins.     H.-rbivorous  animals  secrete  an  alkaline  .nine 
wl.i.h  is  no  do.d.t  caus...l  by  the  pn-s.-nc  of  tl...  large  amount  of 
alkaline  earths  and  th.>  relatively  small  amount  of  l.rot.'in  mat- 
ter in  their  diet.    The  human  urine  becomes  alkaline  in  rea.-tmn 
when  vcKctables  are  the  main  infrredi..nts  of  th.'  diet. 

The  character  of  most  of  the  urinary  eoiistitu..nts  an.l  th..  man- 
„..,•  bv  which  thev  arc  .lerived  from  th."  foo.lsti.tfs  have  b....ii  dc- 
serib.'.l  ill  the  chapt.'r  on  nu'tabolism,  an.l  in  th.-  f.)llowiiig  a-- 
,.ount  only  a  bri..f  r.'vi.'W  of  th.ir  i.hysi.-al  and  eh..mi.-al  natur.' 

is  necessary. 

Tin:  t>R.i.\Nic  SiBSTANC-KS  ov  Tin:  rKiNF..-rii..se  eompris..  a 
number  nf  nitrogenous  compounds.     The  toUowing  figuivs.  ..b- 

229 


-•'^0  l'IIY.sHir,(H)Y   KOB   DKNTAIi   STIDENTS. 

t)iiiic<l  from  til.'  ifsiilts  of  tin-  iiimlysis  of  ii  iiiimlKT  of  iiornial 
iivci-fiKf  urines,  show  liow  flir  nitronni  is  ilisfrihiiti'il  aiiionj.'  thrsc 
i-oinpoiiiulM. 

''•■'•»    S5  to  !»()'; 

Aimiioiiia    2  to     4' ; 

('rcfitiiiin    .  .  ;{»^ 

'''•'<•  'K'i'l    1   to     2'/, 

I'lu'lassificd  nitrop-n .'>  to    6% 

r/7(j.— Krorii  thf  iihovc  fiKUivs  it  is  sfcii  tiuit  tiit-  Ki-cattT  part 
of  the  nitrofri'ii  cliniinHtcd  l)y  man  ai)p(ars  as  urea.  The  relative 
amount  of  iii-ea  eliminated  depends  very  larjfely  on  the  diet,  be- 
ing !»0  ])er  eent  or  more  of  the  total  nitrojjen  exeretion  on  a  full 
•  HOtein  diet,  and  «()  per  cent  or  less  during  starvation.  The  total 
amount  exereted  is  about  :{0  fjrams  |»er  100  (jrams  of  protein  in 
the  diet. 

Cliemicaliy  urea  has  the  following,'  formula  : 

-Ml, 

OC 

\ 
Ml, 

If  prepared  pure  it  forms  long  colorless  needles  or  four-sided 
prisms.  It  is  very  soluble  in  water.  Hot  alkalies,  sueh  as  sodium 
hydoxide.  deeompose  it  into  ammonia  and  carbon  dioxide.  The 
same  reaction  occurs  in  case  of  bacterial  decomposition  by  the 
niicrococcns  urea,  and  accounts  for  the  ammonical  odor  of  urine 
after  standing  in  the  air.  The  significance  of  urea  in  regard  to 
I)rotein  metabolism  and  the  method  of  its  formation  are  dis- 
cu.ssed  on  page  lOS. 

Ammoitid. — This.  cond)ined  with  chlorine  or  oth.-r  acid  radi- 
cles, is  normally  found  in  small  amounts  in  the  urine.  It  is  one 
of  the  important  agei:cies  in  maintaining  the  neutrality  of  the 
tissues,  since  with  acids  it  forms  ammonia  salts,  which  are  neu- 
tral in  reaction  and  which  are  eliminated  in  the  urine. 

('natiniu.—Tht'  amount  of  this  substance  found  in  the  urine 


THE   (•|lKMI>'rKY   HI-'    rUINK. 


:M 


IS  vt 


TV  constant  from  day  to  day,  am 


I  is  iiidcpcndrnt  of  tlir  <lift. 


It  is  {ar«.'ly  a  product  of  the  m.taholism  of  Hi-  U»\y  tissues 


I'ric 


.1(1'/.— I'ric  ac 


I   is  a  iiurim-  luid.s    and   its  n 


lationsliip 


to  tho  other  purines,  and  its  mo i 

fullv  discussed  in  the  ehapt.'r  on  im 


ire 


relatively  insolidile  in  \va 


ter.  and  when 


f  formation  and  si^niticanee 

■taholism  '  p.  11'*  ••    It  IN 

dlowe.j   ti)  erystali/.e  it 


forn\s  small'  rhom 


hie  crystals.     It  .an  unite  with  an  alkuli,  such 


80<li\un  hydroxi<le.  to  torm  two  sa 


as 
sodium  ( 


lt^ 


neutral  or  diurate  ot 


C.Il.N.O.Na.)  and  tlie  hiiirate  or  a( 


((  ,ILN,(),UNa). 


The  hiiini 


id  urate  of  .sodium 
nd 


^.s  are  neutral  in  reaction  and  eo 


stitute  the  urates  norma 


ally  found  in  the  lilood  and  urine 


Th: 


ex 


ist  in  two  isomeric  forms 


((/  and  the  /*  1 
the  dt 


The  /)  is  more  solu 
)f  \irate  tar 


1,1,.  than  th.-  <,  form.  It  may  he  that  the  deposition  ot  urate  i; 
tar  on  the  t.'cth.  an.l  the  ,h-posits  of  urates  in  the  .mints  ot  a  pa- 
tient .sutferinjr  Nvith  «out,  are  due  t.,  tiie  chaii-e  of  the  o  torm 
into  the  less  soluhh'  u  type. 

There  are  a  numher  of  oth.^r  nitrogenous  h..dies  in  the  urme 
which  are  inclu.led  in  the  item  ..f  un.-lassitie.l  nitroji,.,,  „,  the 
ahove  analysis.  The  most  important  of  these  is  urinary  iiulican. 
which  is.l.-rived  frmu  th.-  indol  pro.luced  in  the  mtestm.-s  l.y  the 
action  of  bacteria  mi  the  amino  aei.l  trytophaiie      Tn..  yellow 

color  of  the  urine  is  prod.ice.l  l.y  a  i.i^' nt  called   uroehrome. 

xvhicli  is  helieved  t..  he  .lerived  imm  the  pi-no  nts  m  th.'  hlood. 
Ti.K  lN..K.iANU-  ('..NSTrnKN-^  nK  TiiK  liiiNK.-Th"  uruiary 
salts  are  chi.-fly  the  chlori.les.  suli-hates  an.l   phosphi-t..s  ..t  s..- 
dium,  potassium,  .alcium  an.l  matfiiesiiim.     The  i-otassuim  an.l 
so.lium  salts  aiv  fmiii.l  in  y.vat.'st  al.un.lan.-.'.  simv  tli.-y   Inrin 
the  main  inorganic  .-oiLstitueiit  of  th.'   f.m.l.  an.l   im.iv.nvr  th.. 
Kirater  portion  ..f  the  salts  of  tii.^  h.avi.'r  m..tals.  as  .•al.-ium.  ir.oi. 
bismuth.  m.Tcury.  .-tc  is  ..xcn't.^l  l.y  the  iiit..stiii..s.      rh.'!-  is 
yerv  little  retentim.  ..f  salts  l.y  th.^  l..'..ly  ex.-.-i.t  .lurinj,'  the  tor- 
nation  of  bmi.'.  so  that  the  amount  of  the  iimr-ainc  cmistitu.Mits  ot 
urine  vari.-s  fn.m  .lay  t..  .lay  with  th.^  .liet.     Th.'  .-hlon.l.'s  air 
forim..l  for  th.-  nu.st   part    fn.m  tl...  inor-an..'  ehl..n.l.-s  ..t    tl„. 
food;  the  phosphates  an.l  th..  suli-haL's  aiv  .l-nv.,!  tn.m  th."  sul- 
phur  and   idH.spliorus  of  the   .mcl.-o-prot-n.    .....h.-uh's.      M    the 

urine  is  n.-utral  ..r  alkaline  in  r.'acti..n.  theiv  is  ai.t  t..  l.>   a  .1.- 


If 


Si2 


i'llY.sllll.iMiV    Kull    IlKNT.M-    >TI  DKNTS. 


■1 


jiosit,  of  <'iilciiiin  or  iiiiiu'iKsiinn  plmspluifr.  This  will  .|i.s.siilv.- 
whfii  till-  urine  is  r.rnlcr.d  faiiitly  iici.l. 

AhNmUMAI,    CnXSTITl  KNTs    ny    TMi:    rK|.M:._.Ma„ v    „(    thr    Mil,. 

stjiMn-s  found  in  tli.-  hloo,|  ,„-,.nr  in  niiinit.-  tnicrs  in  Wu-  urin... 
Wh.'n  imy  of  tii.-s.-  l)<),ii,H  jnv  incr.-asc.l  to  an  unusual  annMUil 
in  tin-  urine,  they  Ix-com.'  what   we  may  term  pathitlo^ieal  mu- 

stituents.     The  ho.lies  most  eoi ,nly  atVeete.!  are  the  proteins 

an.I  sup.rs.  The  fin.linjr  of  a  |.rot..in  sue!,  as  all.umin.  in  m.wv 
than  the  faintest  trace,  is  an  indication  of  luphrilis  or  l{ri,/hfs 
(iisrasr.  The  presence  of  alhumin  may  he  detectd  |,y  lieatinjr  h. 
a  t.-st  tube  a  slightly  aci.Julated  sample  of  urine. 

Normal  urine  contains  the  faintest  trace  (.f  the  l.lood  suyar 
(h-xtros.-.  hut  in  ahnormal  conditions,  as  in  tlie  disease  ,ii,il„l,s 
or  after  h  meal  rich  in  sugars,  a  larjre  amount  of  dexiros,.  ap- 
Itears  in  the  urine  as  a  result  of  an  increase  in  the  sHn»r  of  the 
blood.  The  condition  probably  repr.'.sents  tli.  inalulitv  „(  th.- 
tissues  to  make  us.'  of  their  carbohydmte  f.,od  in  the  proi.er  man- 
ner, and  the  kidney  thendore  excretes  \hv  sujjar  as  if  it  wen-  a 
waste  nuiterial. 

The  Organs  of  Excretion,  The  Kidneys. 

Projecting  from  the  jmst.'rior  wall  ..i  the  abdumina!  cavity  at 
th.'  level  of  the  lower  ribs  and  on  each  side  „f  the  vertebral  col- 
umn  ar..  the  kidneys,  the  organs  of  urine  excretion.  Kadi  kidiirv 
is  of  the  nature  of  a  tubular  gland  of  a  very  complex  striietuiv. 
anatomically  adapted  to  bring  a  large  amount  of  blood  at  ,i  hi-di 
pn'ssure  in  close  relation  with  the  excn  ting  epithelial  cells  which 

'  ♦'"'  ^^"""-^  "f  the  gland  Inhuhs.     The  tubul,.s  emptv  into  a 

jmuch-shaped  sac  on  the  ini:.-r  e.lge  ,d'  the  kidney,  the  pelvis 
of  the  kidney,  and  this  is  connecti'd  with  the  iiriiiarv  bi.idder  bv 
means  of  a  small  tube,  the  ureter. 

A  brief  review  of  the  essential  {)arts  of  the  uriniferous  tubuh' 
and  the  organs  of  micturition  is  ...■•v^,,.rv  in  ord..r  to  underst.'Md 
liie  mechanism  of  urine  excn^tion.  and  iU  student  is  advise.l  to 
consult  his  textbook  of  anatomy  and  lii.stoin^^v  for  a  mor..  .-om- 
prehensive  desciiption  than  is  li.ie  ^iv,n.  The  urinif.rous  tu- 
bules may  be  divide.!  int.,  (h ...r.-tory  portion  ;m.l  th..  coll.-ct- 

ing  portion.     The  tubules  arise  in  the  outer  j.art  of  tn,.  ki.|ii..y 


m 


if'  U 


Q' 


'  i 


Kit?,    ST. — KhiKiiim  iif   tlif   \iiiiiiriTinis    luliuli'S    (I. luck),    the   aiti-ilcs    (icil) 
;iriil  till'   Veins    (liiui-)    iif  tlie  kiilinv. 


THE  EXCRETION   OP   TRINE. 


233 


in  the  region  called  the  cortex,  as  a  body  calli-d  tin-  .Miilpit,'liian 
corpuscle.  This  corpuscle  consists  of  the  dilated  nid  of  a  tul)ule 
whicii  is  invaKinated  to  form  a  e>ip-sliaped  vessel,  witliin  the  cup 
of  which  lies  a  tuft  of  capillaries.  The  eapiilarifs  compose  llir 
structure  known  as  the  glomeridu.s,  and  tiie  tubular  part,  tlir 
capsule  of  Hownuin. 

Prom  Bowman's  eapside  a  short  neck  leads  into  what  is  known 
as  the  convoluted  tubule,  which  is  a  very  tortuous  vessel  lined 
with  very  large  ei)ithelial  cells.  This  structure  lies  in  the  cortex 
of  the  kidney  and  is  nourished  by  the  blood  which  has  already 
been  through  the  glomerular  capillaries.  A  loop  of  the  tubule 
leads  down  into  the  center  or  medullary  portion  of  the  kidney 
and  back  again  to  the  cortex,  where  the  cortex  again  becomes 
very  tortuous.  This  finally  empties,  in  company  with  many  otie  i- 
.siuular  vessels,  into  a  common  collecting  tubuh',  which  leads  to 
the  pelvis  of  the  kidney. 

TiiK  Bi,(W)i)  Sii'i'iA-  OK  THE  Km)\i;v  is  very  large  compared 
with  that  of  the  other  organs  of  the  same  size.  The  renal  arteiiis 
come  from  the  aorta  and  distribute  their  blood  directly  to  the 
glomeruli  and  the  inner  medullary  jwrtions  of  the  kidney.  The 
ves.sels  of  the  glomerulus  are  collected  into  an  afferent  vein,  which 
again  breaks  up  into  capillaries  to  sup])ly  the  remaining  struc- 
tures of  the  cortical  portions  of  the  kidney  (Fig.  .{7). 

The  Xerves  of  the  Kidnev. — The  ki<lni"y  is  very  richly  sup- 
plied with  vasomotor  nerve  fibers,  which  are  cai'ried  to  it  in  the 
splanchnic  nerves.  Whether  there  are  nerve  fibers  in  either  the 
vagus  or  splanchnic  nerves  which  have  a  secretory  inflneiice  on 
the  kidney  cells,  is  at  present  an  unsettled  ipiestion. 

The  Nature  of  Urine  Excretion.— In  si>ite  of  the  many  at 
tempts  to  explain  the  nature  of  urine  excretion,  there  remain 
many  steps  in  the  process  which  are  not  fully  undeistood.  The 
con.stitueiits  of  the  urine  are  formed  by  other  organs  than  the 
kidney,  and  are  present  in  the  blood  plasma.  Tlu;  function  of 
the  kidney  is  to  remove  the.se  .substances  from  the  blood.  .Many 
bodies  are  j)resent  in  the  blcod  i)lasma  which  are  imt  found  in  the 
urine,  and  again  some  of  the  urinary  constituents  are  found  in 
far  greater  concentration  in  the  urine  than  in  the  blood  plasma. 


2U 


I'llYSIOI/HlV    Vim   DK.VTAr^    STI'DKXTS. 


To  ('xj)laiii  these  fncts.  Ludwig.  a  famous  physiolofrist  of  the 
iiiiieteeiitli  eeiitury.  foritiiilated  what  is  known  as  the  nieehanieal 
theory  of  urine  exeretion.  Impressed  hy  the  peeuiiar  rel:itioii- 
sliip  of  Bowman's  eapsuh-  ami  the  jrlomerular  eaj)inaries,  he  eon- 
ehuh-d  tliat  tlie  .Malpi^liian  eorpusele  is  a  filterinfi  apparatus 
whieh  sejjarates.  in  dilute  solution,  a  portion  of  all  the  ditfusihle 
suhstaiices  of  the  blood.  The  absenee  of  sueli  diffusible  sub- 
stances as  sujfar  in  nornu'!  urine  and  its  presence  in  th<'  blood  in 
a  relatively  lar^'e  amount.  \\<-  believed  to  be  due  to  the  ability  of 
the  epithelium  of  the  tubules  to  reabsorb  these  substances  from 
the  dilute  urine.  Likewise,  the  hiifh  concentration  of  .salts  and 
nitrogenous  bodies,  such  as  urea,  he  explained  by  reabsorption 
of  water  through  the  tubules  into  the  bhxxl.  In  supi)ort  of  tliis 
theory  Lmlwig  demonsti-ated  that  the  urine  excretion  varied 
directly  with  the  blood  flow  and  the  blocMl  pressure  of  the  kid- 
ney. In  other  words,  the  great.-r  the  su|)ply  of  blood  and  the 
greater  its  itressnre.  the  more  rapidly  will  the  watery  solution 
of  flu  urine  be  filtered  from  the  blood.  He  was  not  able,  how- 
ever to  bring  any  satisfactory  |)roof  of  the  reabsorption  of  water 
or  other  .substances  by  tin-  epithelium  of  the  urinary  tubules. 
Indeed,  most  experiments  show  that  this  does  m)t  iccur. 

It  is  impossible  to  exj)lain  all  the  facts  of  urinary  excretion 
by  simple  physical  laws.  For  example,  urea  and  dextrose  are 
both  found  in  the  blood  and  both  obey  the  same  pliysico-cheniical 
laws:  nevertheless  the  one  is  excreted  in  the  urine  and  the  other 
is  retained  in  the  blood.  Furthermore,  when  certain  |(igments 
are  injected  into  the  blood,  they  are  excreted  by  the  kidney  cells, 
but  do  not  ajipear  in  tho.se  of  other  parts  of  the  bod-. 

That  an  increase  in  the  i)res.sure  of  blood  in  the  renal  vessels 
has  a  very  marked  accelerating  effect  on  the  excretion  of  urine, 
is  not  necessarily  evidence  that  the  increased  blood  supply  is  the 
cause  of  the  excretion.  That  other  factors  are  concerned  is  demon- 
.strated  by  the  action  of  drugs  which  cause  an  increase  in  renal  ex- 
eretion. For  example,  digitalis,  a  drug  stimulating  the  circulatory 
ai)paratus,  causes  a  marked  <liun'sis  in  cases  of  a  weak  heart 
where  the  pres.sure  has  been  totally  iiiadei|uate  to  maintain  a 
urine  excretion,  but  has  little  or  no  action  on  the  noi'mal  kidncv. 


TIIK  EXCHKTION   oK   rUINK. 


235 


Oil   the   othiT   liaiid.   soditim    su1i)liat('   iiijccttMl    into   the   Mood 
causes  a  diun-sis  vvitlio\it   marked  cliauj.'.'  in  ral.'  of  blood  flow 
,)!•  l)lood  pivssuiv  by  diivct  stimuhition  of  tlie  ivnal  epitbeliuni. 
In  almost  every  ease,  moreover,  an  increase  in  the  excretion  of 
urine  is  followed  by  an  inenas.'  in  the  amount  of  oxvgeii  us.'d 
up  by  the  kidney.     It  is  a  jieii.'ral  law  that  every  increase  in  cell 
activitv  is  accompanied  by  an  increase  in  the  amount  of  oxyKcn 
used  by  the  orfjan.  and  the  increas.Ml  l.l(M)d  flow  accompanying,' 
most  forms  of  diuresis  is  readily  explained  on  the  basis  of  the 
physiological  need  of  the  tissue  for  watei'  and  oxy-j.  n.     If  physi- 
cal laws  w.-re  sufficient  to  explain  all  tli-    phenomena  of  excre- 
tion, there  would  be  no  need  for  oxygen  in  in-Mvased  amounts 
during  periods  of  iiicr.as.'<l  urine  formation.     A  conc.-ption  of 
the  actual  amouni  of  work  which  the  cells  must  do  to  e.xcrete  the 
urine  mav  be  obtained  by  comparing  tin-  osmotic  pressure  of  the 
ur-."  with  that  of  tlu'  blood.     The  osmotic  pn-s.sure  of  the  blood 
'-  half  that  of  the  urine,  and  for  each  one  thousand  cubic 
...,      .letres  excreted,  it  is  sutfiei.'iit  to  call  for  th<'  .xpenditure. 
:•,.  part   of  the  renal   cells,  of  a   force  capable  of  lifting  a 
)„und  through  one  thousand  feet. 

We  may  conclude  that  the  natur.'  of  the  excretory  mechanism 
cannot  bo  explained  by  the  pliysico-chemieal  laws  as  we  now 
know  them.  i.  e..  the  phenomena  of  osmosis,  filtration,  absorption, 
etc.,  but  rather  that  it  must  be  dm-  to  a  vital  actimi  on  the  i)art 
of  the  renal  cells.  It  is  this  vital  function  of  the  cells  which 
enables  them  to  remove  on."  substance  frmii  the  blood  and  to  leave 
another  which  is  identically  the  same  so  far  as  physieo-chemica! 
properties  are  concerned. 

Micturition.— The  urine  diseharg.'d  from  the  collecting 
tubules  of  the  kidney  into  the  pelvis,  is  carried  to  the  urinary 
bladder  through  the  ureters  (Fig.  :{S).  Tin-  muscular  coats  of 
the  ureter  have  a  movement  similar  to  that  of  the  digestive  canal 
ami  bv  i)eristaltic  waves  force  tlu'  urine  down  through  the  urder 
into  the  bla<lder.  The  urine  thus  collected  by  the  bladder  is 
ivtained  for  a  time  and  is  at  intervals  ejected  through  the  urethra 
by  the  act  of  micturition.  This  consists  of  strong  contraction  of 
tile  bladder  walls,  together  with  the  contraction  of  the  diaphrag- 


•_':{(i 


I'lIYSIOLfKlY    FOR    DENTAL    STl'DENTS. 


iiiiitic  iiiid  iilxloiiiiiial  imisclcs,  the  ffVcct  of  wliich  is  to  rcdui-c  tlic 
size  of  tlir  l)la(l(l('i'  cavity  and  to  v\\h'\  tiic  urine  witii  prcssiirt'. 
tlirou^li  tJR'  iirothra. 

Tiic  act  is  under  nervous  control,  tlie  motor  nerves  being  de- 
ii\ed  from  nerve  cells  found  in  the  lumbar  reifion  of  the  conl. 
'i  i'f  stinuili  here  i)rodueed  co-ordinate  the  nuiscular  movements 
i>i  ihe  act.  The  afferent  or  sensory  stinnili  which  initiate  tin- 
act  ire  excited  by  the  distention  of  the  bladder,  or  by  the  j)ass- 
aj;e  of  a  few  <lroi)s  of  urine  into  the  first  portion  of  the  urethra. 
These  stinuili  pass  to  the  center  in  the  cord  and  are  returned  to 


Verio  cc»Mj 


Aorta 


Kit,'.    :is.  •    I  )iiiKiaiii  III'  uiiiiMiy   svsliiii. 


the  muscles  of  the  blatlder  also  causinf?  the  sphincter,  w  liicli  closes 
the  bladder,  to  be  relaxed.  In  the  voluntary  act  the  nmtor  nerves 
ai'c  stiuMilated  by  impulses  from  the  higher  centers. 

The  Function  of  the  Skin. 

The  skin  serves  a  double  function,  that  of  protecting  the  body 
from   (lie   oiilside  enxii'oiunenl,   and   that   of  excreting  es.scntiai 


Till".   Kl  NCTHlNS  OF  Till'.  SKIN. 


•2M 


fluids  from  its  frlaii.ls.  Contrarv  to  -.■ii.Tal  bcli.-f.  tl...  -lan.ls 
of  tlu-  skin  -lo  not  .-x.'ivtc  tiu-  wast.'  sul.stanccs  of  tl..'  l.u.lv.  ..r 
at  l.sist  .10  ., .  onlv  to  a  v.-ry  liniit.'.l  .If^riv.  Tli.-ir  fun.-tu.ns  any. 
to  m'ulat.-  th.-  int.-n.al  h.-at  of  tlu-  ho.l.v  (sw.-at  -lan.is)  :  t..  h.l.n- 
,.at.' hs  surfa.T  an.l  hairs  (s.^lmn-ous  srlan.lsi  -.  an.l  to  provi.l.-  tl..' 
l„.st   form  of  nourisl.m.-nt   for  th.-  ...■vvl.orn  a......al    ( ...an.n.a.v 

srliiiuls").  ,      ,    I       ,      ( 

The  Sweat  Glands.— Tli.'s.'  aiv  simple  coil"'"'  mLular  stni.'l- 
„,vs.  foun.l  pra.-ticallv  ..v,'.-ywl..Mv  in  tl..-  .-ntan.'ons  tissu.-  ..1  tl..- 
|„ulv  lu-infi  .■sp.-<-iallv  numerous  in  c-rtain  pa.-ts.  as  n.  tl..-  pa  n.s 
„f  tin-  han.ls  an.l  tin-  m.I.-s  of  tl..-  tV.-t.  Tl..-  .-x.-r.-t.i.^'  .-.-Us  hn.- 
tl„-  l..w.-r  porti.ms  of  tin-  tulml.-s.  ..1  a.v  (•o...pos.-.l  ot  -ranular, 
....lumnar  epith.-liun..    Tl..-  fflamls  an-  richly  suppl..-.l  xv.th  n.-rv- 

fihcrs.  . 

The  amm.nt  of  sw.-at  ^'iv.-n  off  in  a  .lay  var..-s  -,vatly.  sn.ee 
it  is  inriu.-nc.-a  l.v  ...any  thinjrs.  as  heat,  n.oi.^tu.-.-.  e.vere.s.-.  .-ioth- 
ing  ete.  (s.-.-  p.  Ur.).    The  perspiration  of  wh.eh  w.-  ar.-  ....eo..- 
seious  amounts  to  a  .-onsi.l.-rabl.-  numb.-.-  of  sra...s  ,.00  to  i>00 
LM-ams)   i..  a  .lav.     Altl..mj.h  it  is  v.-ry  .liHieult  to  obta.n  pu.v 
sw.-at   u..n.ix.-.l  with  tl..-  s.-.-r.-tions  of  tl..-  ..th.-r  -lan.ls  ot    th.- 
skin   we  know  that  it  e.msists  for  tl..-  n.ost  part  of  wat.-r,  hav-.  ff 
a  spi-eifle  fjravitv  of  about  1.004.    Th.-  salty  taste  is  .1...-  to  ...or- 
^a.iie  salts  an.l  to  th.-  in.puriti.-s  whieh  tl..-  sw.-at  .l.ssolv.-s  o..  tl..- 
surfaee  of  th.-  skin.     Tl..-r.-  is  m.ly  a  trae.-  ..f  u.-.-a  an.l  re  at.-.l 
substanees.  an.l  probably  th.-  sw.-at  -lan.ls  n.-ver  ai.l  th.-  k..l...-ys 
in  the  .-xe.-.-tion  of  th.-se  bo.li.-s. 

The  most  in.iM.rtant  function  of  th.-  sw.-at  -lan.ls  .s  t..  .-ontrol 
the  t.-mperatun-  of  th.-  bo.ly  by  r.-srulating  th.-  .-at.-  ot  its  l..-a1 
loss  Dry  air  is  a  po..r  .-on.luetor  ..f  h.-a1.  an.l  to  va|)(.ri/.-  wat.-.- 
n-.,uir..s"a  larjt.-  amount  of  h.-at.  As  th.-  water  of  the  sweat  .s 
.-vaporat,..!.  the  bo.ly  los,-s  heat  rapi.lly.  This  pr.n.-.l.le  is  pra.-ti- 
callv  ai.i.li.-(l  bv  th.-  hous..wiv..s  of  tropi.-al  eountn.-s.  Th.'  wat.-r 
is  lilae.-.l  in  ponnis  pots  an.l  tl..-  rapi.l  .-vap..ration  on  th.-  ...it- 
.si.le  of  the  pot  eools  the  wat.-r  within. 

The  secretion  of  sweat,  lik.-  the  secretion  of  saliva,  is  un.i.-r 
the  .-ontrol  of  th.-  c.-ntral  n.-rv..us  syst.-ni.  as  can  b.-  .l.-nu.nstrat.-.l 
y,y  ^.l,.^.t,•icalh•  exciting  the  nerv.-s  supplying  the  paw  of  a  eat  or 


2:{H 


I'irYSIOlAHiV    FOR    OKXTAI;    STlOr.XTS. 


I,i 


i 


(loj;.  Following  such  stiinulatioii  drops  of  sweat  ai-c  found  on 
tlic  paw.  The  secretion  is  not  due  to  an  increased  Mood  flow,  as 
can  be  shown  by  stiinulatin»r  the  nerves  in  a  iind)  severed  from 
its  blood  sup|)ly,  in  whieli  case  a  few  drops  of  sweat  will  still 
appear.  A  center  in  tiie  brain  and  subsidiary  centers  in  tlie 
sj)inal  cord  have  been  found  which,  when  stimulated,  j)roduce 
a  .secretion  of  sweat. 

Some  drugs  have  the  peculiar  action  of  exciting  the  s<'cretion 
of  sweat,  either  refle.xly  through  the  nerve  center  or  by  stimuia- 
tion  of  the  nerve  endings  about  the  cells  of  the  glands.  To  the 
f(»'mer  clas.s  belong  such  drugs  as  strychnine  and  i)icrotoxin,  and 
to  the  latter,  pilocarpiii.  Atropin,  on  the  other  hand,  iidiibits 
the  .secretion  by  i)aralyzing  the  secretory  nerve  mechanism.  An 
increa.se  in  the  external  temperature  will  cause  a  .secretion  of 
sweat  only  when  the  seii.sory  and  motor  nerves  of  the  j)art  are 
both  functional.  To  stimulate  the  sweat  nei-ves,  heat  therefore 
must  act  refle.xly  through  the  sensory  nerves  and  the  centers  of 
the  brain  or  si)inal  cord. 

The  Seb.vceois  (iL.\.\i).>^. — Uesides  the  sweat  glands  there  an; 
numerous  other  glands  in  the  skin.  These  aiv  as.sociated  with 
the  hairs,  and  are  called  sebaceous  glands.  They  secrete  an  oily 
semili(|uid  uuiterial  which  atl^'ords  protection  to  the  hair  and  the 
skin.  Its  oily  nature  j)revents  the  hair  from  becoming  to<»  brittle, 
and  })rotects  the  skin  from  moisture. 

Tjie  Secrktio.v  of  Mn.K. — The  mammary  glands  are  modified 
sebaceous  glands  which  secrete  a  nutrient  rluid.  milk.  The 
glands  are  much  better  developed  in  the  fenude  than  in  the  male, 
and  are  excited  to  i)liysiological  activity  at  the  birth  of  the  child. 
Human  milk  is  a  white  or  yellowish  fluid,  without  odor  and  with 
a  peculiar  sweet  taste.  It  contains  i)rotein  substances  called 
caseinogeii,  laet-albiuiiin,  and  lact -globulin  ;  also  a  .sugar  called 
lactose  or  milk  .sugar,  and  fats  and  inorganic  matter,  as  the  chlo- 
rides of  sodium,  jiotassium  ami  calcium.  Human  milk  is  by  far 
the  l)est  food  for  the  infant,  and  should  be  replaced  by  other 
food  onlv  when  absolutelv  necessarv. 


CUAPTEU  XXV. 
THE  NKHVOIS  SYSTEM. 

The  General  Functions  p  d  Structure  of  the  Nervous  System. 

— Wlu'ii  a  unicfllular  nrtfa...sMi.  siicli  as  tin-  anm-1)a.  is  stimiilal.'.l 
it  ivspoiuls  l)v  a  inov.M.KM.I  l.r.-ausc  its  |.n.t()|.lasn.  p(.ss..s..rs 
anunifi  its  oth.T  piop.-rti.s  tl.os..  of  .-xcitability.  coiuluctivity  aiul 

contractilitv.     In  tlic  cas.-  of  niulticvlluinr  organisms,  soin. lis 

art"  s.'t  asi(i."  for  the  assimilation  of  food.  oth.Ts  for  niownicnt. 
others  to  ree.-ive  stimuli  from  tiie    outsi.le.    others    to    eomi.ose 
t..ii^'lier    i.roteetive    tissues    on    the  surfa.-e.  and  still  hthers.  in 
many  auinuds.  to  eompose  deHiiite  or-aiis  of  ott'ense.     This  loea- 
tioii'of  speeitie  fuiietions  in  eertai'i  frroup  of  eells  makes  it  neees- 
sarv  for  the  welfare  of  the  orjranism  as  a  whole,  that  some  means 
of  eommunieation  he  provided  between  th."  ditl'erent  parts  of  the 
animal,  for  otherwise  the  cells  whieh  ar.'  oecu|)ie.l.  say,  in  al)- 
.sorhin^r  food,  woul.l  he  unahle  to  move  away  when  some  destruc- 
tive asreiicv  approached  them,  and  in.ie.-d  the  moving  (mns.-h') 
cells  couhi  never  know  when  they  onjrht  to  become  active.     In 
some  of  the  lower  orfranisms  thes..  messa«es  are  carri.-d  by  chemi- 
cal substances  present   in  the  tiuids  tliat  bath.'  the  cells.     These 
lu'long  to  the  uroup  of  hormones  which  we  hav.-  aliva.ly  studied 
in  connection  with  the  ductless  frlamls   (see  p.   12-i).     The  iv- 
spc.nsi's  mediated  in  this  way  are.  however,  too  slow  for  the  .,ui.-k 
adaptMtion  which  it  i.^  necessjiry  that   tin-  (.r-anism  should   un- 
dergo ill  its  battle  for  lit'.-.     If  it  had  to  .lep.'i.d  on  such  a  mech- 
anism alom-.  the  oi-anism  would  alivady  be  within  llw  clutches 
of  its  enemv  before  it  could  mak.'  any  attempt  to  .hdVnd  itsell. 
Some    more    sensitive    mechanism,    both     for    receivinti    and 
for  transmitting  impulses  tliroufihout  the  organism,  becomes  nec- 
essarv.     This  is  furnished  by  the  nervous  system,  which,  in  Us 
simpier  torm.  consists  of  a  c.-ll  on  the  surface  of  the  aniimd  so 
specialized  that  it  i-siionds  to  changes  in  the  .'iivironinent.    This 


240 


I'llVSlOl.OCV    FOR    OrNTAh    STfOKNTS. 


III 

i'  1 


nitphir  ••('11.  as  it  is  ciillcd,  is  i)rolonjr(Ml  inside  tlu'  iiuiinal  as  a 
fiber,  the  lu  rr(  jilu  r.  wliieli  )iasses  to  (ffiriitr  (tils  specializ'-d 
either  as  inuscle  fibers  or  Kbiiid  cells.  Wlx-n  a  stiriiulus  acts  on 
tbe  leei'ittor  Cell  it  therefore  sets  u|)  a  nerve  iiiipulse  whicii  causes 
effector  cells  to  become  active,  so  that  the  animal  either  moves 
away  or  jirepares  to  d.-feiid  it.self  by  seen  fiiij?  some  jioisonous 
substance  or  inakinjr  sonu  defensive  movement.  There  are.  h(»\v- 
ever.  very  few.  even  of  the  lowliest  oi'-ranism.s.  which  have  so 
simple  a  nervous  system  as  this,  for  the  nerve  fibers  from  ditfer- 
ent  recejitors  usuall.v  join  tojiether  to  form  a  mm  iili.nis  and 
tliev  ilo  not  run  directlv  to  the  effector  cell,  but  to  another  <'ell. 


KiK.  ;!'.". — .SclniiiM  <>t  siiiipl"'  i>ll>'X  Mil-;  )' 
Ilium-;  (I.  MtTiiiiit  liliir  :  .v.  s,\  iiiipsis  ;  <.  iiit\. 
hi,  cITfctiii-  iiii;:iii. 


ii'cipliir    ill   Mil    ciiithi'liiil    imiii- 
cill  iif  (-.•iitir;  r,  .■tYfifiit  tibir; 


Hu  C(  niral  uirvt  <tll.  which  is  specialized  as  a  junetiomd  or  dis- 
tributin<?  center,  and  whicli  then  transmits  the  impulse  by  a  fil)er 
of  its  own  to  the  jirojter  effectoi"  orfjans. 

Thus  ivi  litni   till   issiiiliiil  ilnniiih  of  llir  so-mllnl  r(fl<.r  iiri 
{Vi^.  ;{!•).  that  is.  a  receptor  connected  with  a  nerve  fiber  called 

afi(  rnit  ruunin<;  to  a  central  nerv( II  which  is  a^ain  connecti-d 

with  a  nerve  fiber  called  ijjinul,  which  pas.ses  to  some  effector 
organ.  In  certain  of  the  lower  orjianisms  these  nerves  and  nerve 
cells  are  continuous  throuKhont,  but  in  the  hiirher  animals  thi- 
fibers  originating  from  each  coll  do  not  actually  join  with  those 


(iKNKHAI.  STHl  (TIKK   OK   Tlir.    NKUVOIS  sYSTI-.M. 


241 


of  (itli.Ts,  l.ut  only  com.'  in  clas.-  contact  with  thcni.  Tlicy  arc 
c.mtitfiioiis  l)iit  not  continuous,  and  tlic  ncvvc  impulses  pass  from 
th.'  one  to  tlu-  otli.-r  l.v  contact  rather  than  by  transmission 
through  continuous  tissue. 

Kvcry  nerve  cell  jrivcs  ot^"  at  least  one  process  called  th.-  axon, 
and  it  is  this  which  forms  the  axis  cylinder  of  the  n.-rve  til..'r. 
There  an-  usually  other  proc.-sses.  hut  they  ditTcr  from  th.-  axon 
in  that  they  branch  freely  and  do  not  run  for  any  distance  from 
the  cell.    Th.'V  are  called  (lni(lrit(s.    The  axon  may  also  occasion- 
idly  (iive  otr  a  hranch.  oft.Mi  called  a  collnh  ml,  but  it  is  not  until 
it  has  reached  the  etreetor  or^au  or  soiiu-  other  nerve  cell  that 
th."  hranchiiiK  is  pronouncrd.     It  now  bn-aks  up  into  a  mass  of 
Hue  branches.     When  these  occur  at  a  second  nerve  cell,  they 
eloselv  encircle  the  cell,  fornunn  a  basket-like  structure  aronml 
it.    This  is  called  a  >///((//«/>.    The  nerv.-  impulse  can  travel  from 
th.-  Hber  throuj;li  its  syna|>sis  on  to  th.-  n.-rve  cell,  which  this  sur- 
roun.ls.  but  it  cannot  trav.-l  in  tin-  oi)posite  direction.    This  valve- 
like action  at  the  synapsis  explains  why  a  nerve  impulse  trav.-ls 
along  a  refl.-x  arc  in  on.-  .lir.-.-tion  .mly.     Each  nerv.-  c.-ll  with 
its  axon  and  d.-n.lrit.-s  is  call.-.l  a  nniron,.    U.-f1.-x  arcs  are  th.-n- 
fore  comp.is.-.l  of  two  or  mor.-  neui-on.-s.  a!i.l  th.-  n.-rvous  syst.-m 
is  built  ui>  of  ^'reat  nundx-rs  of  r.-flex  arcs. 

Th.-  nerve  cells  which  constitute  the  centers  are  usually  eol- 
l,-<-t.-.l  in  t?roui).s  call.-.l  ,ian„lio.     In  th.-  s.-gm.-nte,l  invertebrat.-s, 
such  as  the  worms  an.l  crustac.-ans.  then-  is  on.-  such  fjanfilion 
for  each  segm.-nt.  .-a<-h  Kan{rli.)n  b.-insr  conn.rt.-.l  with  its  neijrh- 
hoi-s  l)v  nerve  fib.-rs.  thus  forming  a   chain  along  th.-  ventral 
asp.-et  of  the  animal,  and  also  having  num.-rous  nerv.-  fibers  con- 
n.'cting  it  with  the  various  r.-c.-ptors  and  .-tT.-etors  of  t!i.-  K.-gment 
(Fif.  40).    At  the  h.-ad  .-nd  of  th.-  aidnnd  s.-v.-ral  of  these  gang- 
lia become  fuse.l  together  tr  form  a  larg.-r  ganglion,  which  li.-s 
just  behind  the  gull.-t  an.l  from  which  two  fib.-rs  pass  around  the 
gullet  to  nidte  in  front  of  it  in  a  large  ganglion,  which  usually 
shows  thrcv  lob.-s.     Th.-s.-  larg.-r  h.-a.l  ganglia  r.-ceiv.-  the  afT.r- 
ent  nerve  tibn-s    from    th.-    a.l.jac.-nt    pro,jicient    sense    organs, 
n-imelv.  the  eves,  the  ears,  the  organ  of  smell,  and  the  antenna- 
or   feelers:    tiies.»    being   really    receptors   which   have    become 


242 


I'llVSlor.iMiY    Kol{    HKNTAI,    sTI  l>i;\T.'>. 


hijfhly  s|itfiiilizc(|  for  tin-  j)Ui'|>(isi-  of  i-ccciv- 
in<;  impn-ssioiis  from  ii  <listiincc.  .M.iiiy  of 
the  i'tVcrciit  HIhtn  wliicli  iirisc  from  \\u-  cells 
of  tlic  lii'iid  naiijjlia  no  to  the  muisclt's  wliicli 
move  tln'  hijiil  tiid  of  tilt'  animal,  others,  how- 
ever, ilo  not  niii  ilii'eetly  to  eft'eetors.  hut  they 
run  down  the  nerve  chain  to  make  synaptic 

connection  with  tin lis  of  some  of  the  sej;- 

meiital  nanjrlia.  This  connection  of  the  cells 
of  the  head  jianjrlia  with  those  siipplyinK  the 
sejjments  enables  the  former  to  exevcise  a  dom- 
inatirijj  influence  ovei-  the  activities  of  the  lat- 
ter, the  purpose  heintj  that  approachinj;  dan- 
•rers  may  have  a  ^rreatei-  influence  in  deter- 
nuiiin^?  the  response  of  the  animal  than  stim- 
uli that  are  merely  local.  When,  for  i'.\am])le 
some  sight  or  sound  of  an  approachinj;  enemy 
is  receivi'd  by  the  head  ganjrlia,  these  will 
transmit  impulses  down  the  naufflion  chain 
which  so  influence  the  various  nerve  cells  as  to 
produce,  in  all  of  th  m.  a  co-ordinated  action 
for  the  j)urpose  of  j;,,  <tii\fi  the  animal  out  of 
danirer.  Kveii  should  some  local  stimulus  be 
actiufj  on  one  or  more  of  the  sefjments.  the 
stinuilus  which  is  received  through  the  head 
ganglia  will  obtain  the  u))per  hand  and  annul 
or  inhibit  the  local  influence.  The  part  will 
beeome  subs«'rvient  to  the  whole.  This  illus- 
trates the  inlit/nitio)!  of  thi  turraiis  sushui, 
which,  as  we  i)ass  to  higher  animals,  we  shall 
find  to  beeome  more  and  more  develoi)ed  and 
intricate. 

So  far.  however,  the  nervous  I'eaction  is 
|)urely  of  the  nature  of  a  refle.x ;  but  in  the 
highei'  aninuds  other  factors,  namely,  mcmortj 
and  rolition,  come  to  exercise  a  dominating  in- 
fluence on  the  nature  of  tire  response.     The 


KiK.  411.  —  Dia- 
KiuiTi  of  nervuu.s 
system  of  seKnient- 
1(1  invt'itebiate  :  ii. 
s  u  ]i  riKjesojihiigtal 
KiiiiKlion ;  b.  Huli- 
o'.soiiliMKeul  KiiriK- 
lum ;  OP,  (psopha- 
t?U8  or  gullet. 


UKNK.RAI.  STHrCTIUK   UK   TIIK    NKHViMS   SYSTKM. 


24n 


iifTt-rciit  stiimiliis  arriving.  1ft  us  suppose  at  m.tv.'  i-t-lls  (•(.iitioll 
iiifj  tilt'  inovciiifiits  of  till-  l<'«.  iiiav  fail  to  cans.,  a  ivspmis.'  of  tli.' 
(•orrfS|M)inliiitf  iiiuhi'Ics  hi'causi-  of    impulses    imaiiwliilc    traiis- 
luittt'tl  from  hijriicr  iiifiiiorv   ccuters,  for  the  auimal   may   have 
learned  by  experience  that  sueli  a  movement  -is  the  local  stim- 
\ilus  would  in  itself  call  forth,  is  hurtful  to  its  own  hest   ir.ter- 
ests.     This  ex|)erienee  will  have  become  stored  away  as  a  mem 
ory  in  the  hiffher  (memory)  nerve  centi-rs.  so  that  whenever  the 
local  stimulus  comes  to  be  repeated,    impulses    are    disehar-ied 
from  these  memory  t-enters  to  the  local  nerve  center  and  the  n- 
flex  response  does  not  occur,  or  is  nnich  modified  in  nature.    For 
storing  away  these  menmries  and  for  related  psycholojiieal  |)nie- 
csses  of  volition,  etc..  the  anterior  portions  of  the  nervous  systiin 
in  the  vertebrates  beconu'  very     Ijrhly  developed  so  as  to  consti- 
tute the  brain,  and  the  simple     hain  of  <raiu.rlia  of  the  inverte- 
brates conies  to  be  replaced  by  the  spiiiiil  tonl. 

As  we  ascend  the  scale  of  the  vertebrates,  the  brain  beeom.s 
more  and  more  developed,  until  in  the  higher  mammalia,  such 
as  man,  very  few  reflex  actions  can  occur  inde|)eiidently  of  lb'' 
hi^'her  centers  which  are  located  in  it.  In  other  wonls.  the  reflex 
arc  now  involves,  not  one  nerve  center,  but  several  and  of  these 
the  most  important  are  located  in  the  brain. 


r^^^^T'^^r'^STrssBr 


'P 


•  IIAF'TKR  XX Vi 
TIIK  NKUVOI'S  SYSTKM  (((.iii  .1 
Reflex  Action. 

The  Nerve  Structure  Involved  in  the  Reflexes  of  the  Higher 
Mammals.  -In  Kcncrnl.  as  !ilrt'ii<ly  mk-iU  >ii(iI.  tlics.'  incliidc  a 
receptor,  an  afferent  fiber,  a  i.erve  eenl- r,  .  h  efferenl  filler  and 
an  etVeetor  orjfan. 

Thk  KkckI'Tok. — The  reee|iti)r  e.xist.s  M  one  of  tin  si-nsorv 
nerve  terininators  situated  in  the  skin  (extero-eejitorsi  or  in  the 
ili-ep  tissues,  such  as  the  joints,  the  .inscles  or  the  vis<'era 
(pr.)prio-eept.  rs).  Many  receptors  are  inj.'hl.\  speciali/ed  so  as 
to  respoml  only  to  ono  kind  of  stiuiuhi-;,  and  v.n-h  special  kind 
of  receptor  is  located  where  it  will  he  of  nio-st  use.  Thus,  there 
ail'  special  receptors  for  s«'nsations  i)f  heat,  others  for  cold.  oth'Ts 
for  touch.  othcfH  for  pain.  The  /  In  ncrptor^  are  distributed 
more  or  less  uniforndy  over  the  bmly.  Tiiey  ar'-  jiresent  in  tlu 
dee|)er  structures,  such  as  the  teeth,  the  .joints  and  the  sero\is 
coverinjfs  of  tiie  vi.scera.  Sonietintes.  as  on  the  ci  rnea  and  in  the 
pulp  of  the  teeth,  they  are  the  only  kind  of  >  -ceptor  i)resent 
The  touch  ncrptors  are  collected  in  small  ai''  called  "touch 
spots."  which  are  mudi  more  numerous  on  the  .  of  tl  tongue, 
the  lips,  or  the  tips  of  the  finjfers  than  on  thi  ^-'.n  of  tlie  lejf- 
the  arms  or  the  back  of  t!)<  trunk.  The  fre(|U«ii<  »  f  toinh  .spot- 
on  the  tip  of  tile  tongue  inaiies  a  foreign  bo':  ii  'Ik  mouth  ap 
pear  to  be  larger  than  when  we  feel  it  wth 
touch  spots  on  the  fingi  r  tips  may  acijuir  :.'r. 
eeption  by  education,  as  in  'he  ca.se  of  a  bii"i 
to  use  his  fingers  for  reading.  The  remark 
distribution  of  touch  spots  may  he  very  bcis 
finding  out  how  far  apart  the  points  of  a  pai 
1h>  from  one  anoflier  in  order  to  be  di.stinir 
This  distance  is  not  more  than  ;'  mm.  for  the  tij'S  o 


i    lingers 

Til.- 

t  acuity  i- 

|).T- 

[)crson.    \i   ■ 

ll.lS 

irn      birt: 

r    of 

ifuli         itw- 

by 

>f  ealii 

if:           ilS       ■ 

2M 


I 


Ki(f.  41. — Thf  siinplisf  ifrUx  iiic  in  tin-  spiiiiil  niiil.  (  Aflii-  KiHIikor. ) 
Till'  iifTiTcTit  tlliir  in  tlif  piisli'iior  loot  (In  l)lii<k  )  Kivis  off  ciilIalti'Mls.  wliii  li 
ind  liy  syiiMpsi'S  Minunil  tlic  ci'lls  i>r  the  aiilii'iiir  limii  i  in  nd).  the  axnns 
iif  whicli  fiirin  tlif  clTiirnl  lilnis  of  tin-  aritt'iior  loots.  ( Knitii  Howi'll's 
riiysiolos.v. ) 


REFLEX  ACT1«>N. 


245 


but  it  is  over  60  mm.  for  the  skin  of  tho  back  of  tl\t'  iifck.  Tlic 
tvmpf  rat  tire  naptors  arc  still  more  definitely  located  in  areas, 
some  "iH'ing  specialized  for  heat  and  others  for  cold.  These  so- 
called  heat  and  cold  spots  are  most  frequent  on  the  portions  of 
the  bmly  that  are  covered  by  clothing,  for  example,  the  skin  of 
the  thorax,  than  on  thoye  that  are  exposed,  for  example,  the  face. 
They  arc  fairly  frequent  on  the  skin  of  the  dorsum  of  the  hand, 
where  their  existence  can  be  very  easily  demonstrated  by  slowly 
drawing  a  pencil  gently  over  the  sidn.  At  certain  places  tlu^ 
point  of  the  pencil  feels  hot,  at  othei-s  cold,  and  in  others  it 
causes  no  temperature  sensation  whatsoever. 

All  varieties  of  receptors  are  present  on  the  skin  of  the  hand, 
but  in  certain  dis«'ases  of  the  nerves  or  spinal  cord,  one  kinil  of 
receptor  may  become  inactive,  thus  causing,  when  the  absent  sen- 
sation is  that  of  pain,  the  condition  called  andUfrsiu,  which  nuist 
be  distinguisiied  from  that  of  ancsthtsia,  when  all  sensations  are 
paralyzed.     In  analgesia  a  pin  prick  causes  only  a  sen.sation  of 
touch.     When  the  nerves  of  the  arm  are  cut  and  the  cut  ends 
then  sutured  together  so  that  the  nerve  fibers  regenerate  the  skin 
sensations  do  not  all  return  at  the  same  time.  Those  of  pain  and 
of  extreme  degrees  of  heat  and  cold  return  in  from  six  to  twenty- 
six  weeks,  whereas  those  of  touch  and  th.    iiner  degrees  of  tem- 
I)erature  do  not  return  until  after  one  or  two  years.    The  power 
of  localizing  the  point  of  application  of  the  stimulus  is  also  late 
in  returning:  thus,  if  we  touch  the  finger  of  such  a  person  and 
ask  him  to  tell  us  where,  he  may  indicate  some  spot  that  is  quite 
a  distance  away  from  the  one  actually  touched.     Certain  drugs, 
such  as  cocaine,  have  the  power,  when  applied  locally,  of  ren- 
dering all  the  receptors  insensitive. 

The  Afferent  Fibre.— Another  name  for  this  is  the  sensory 
nerve,  because  it  carries  the  sensations  received  by  the  receptors 
up  to  the  nerve  center.  All  afferent  fibers  enter  the  spinal  cord  i)y 
the  posttrior  turve  roots,  on  each  of  which,  it  will  be  remem- 
iM-red,  is  situated  a  ganglion,  the  posterior  root  ganglion.  The 
cells  of  this  ganglion  are  connected  with  the  afferent  fibers  by 
a  short  branch  running  at  right  angles  to  the  latter  (Fig.  41). 
The  function  of  the  cells  is  to  maintain  tho  nutrition  of  the  affer- 


246 


PHYSIOLOGY   FOR   DENTAL   STinENTS. 


1 


:  I' I 


cut  fibers,  for  if  tlieso  bo  divided  before  tliey  reaeh  the  ganglion, 
the  periplieral  or  far  away  t'lid  an<lergroos  degeneration,  whereas 
if  tlie  cut  be  niad»'  between  tlie  ganglion  and  tlio  cord,  degenera- 
tion occurs  central-w.-'rds.  that  is,  towards  and  into  the  cord.  Tl'.is 
degiMieration  always  occurs  in  the  portion  of  the  nerve  fiber  which 
has  Ih'CU  disconnected  from  the  nerve  cill.  It  therefore  furn- 
ishes us  with  a  ready  method  for  finding  out  whetlu-r  tiie  fiber 
is  running  towards  or  away  from  tlie  brain.  In  tlie  former  case, 
the  fiber  is  .said  to  be  ascending,  and  it  degenerates  above  the 
section;  in  the  latter  case,  it  is  descending  and  it  degenerates 
below  the  section.  Since  degenerated  nerve  fillers  give  charac- 
teristic staining  reactions,  we  are  thus  furnished  with  a  means 
of  finding  out  what  becomes  of  the  aflfereiit  fibers  after  they 
enter  the  cord. 

To  further  trace  the  cour.se  and  connections  of  the  afferent  fib- 
ers ill  the  cord,  we  must  therefore  cut  the  posterior  I'oots  between 
the  ganglion  and  spinal  cord  and  after  a  few  .  eks  kill  the 
animal  and  make  microscopic  examination  of  tli.  cord,  stained 
in  special  ways.  If  we  tak(  a  series  of  such  sections  above  the 
level  at  which  the  posterior  roots  have  been  cut.  we  shall  find 
that  opposite  the  point  of  entiy  of  the  cut  root,  the  degenerated 
fibers  occupy  an  area  near  the  tip  of  the  posterior  horn  of  grey 
matter.  As  we  examine  sections  taken  higher  and  higher  up, 
the  degenerat«'d  area  will  bi'  found  +0  shift  gradually  towards 
the  iiH'dian  fissure,  occupying,  first  of  all.  the  .so-called  postero- 
lateral column,  and  later  the  postero-median  (Fig.  42).  When 
we  get  to  the  mrdulld  ubioiiifdta  or  "liulb."  the  degenerated 
areas  disaiipear  because  the  fibers  have  terminated  by  forming 
synapses  around  the  cells  of  the  two  large  ganglia  which  form 
the  hulgings  seen  on  the  posterior  a.spect  of  this  structure.  The 
fresh  relay  of  nerve  fibers  do  not  degeiii'rate  after  section  of  the 
posterior  roots,  but  by  other  lueans  of  investigation  they  have 
been  found  to  Ix'come  collected  into  a  bundle  called  the  fillrt, 
which  cro.s.ses.  or  decus.sates,  to  the  other  side  of  the  iiie<lulla  ami 
runs  up  through  the  pofis  rtiroJii  ami  cnini  nrrhri,  some  of  the 
fibers  ending  near  the  oj)liv  thalamus,  whilst  others  run  on  to 
the  grey  matter  of  the  motor  areas  of  the  cerebrum. 


KKKI.KX   ACTION. 


247 


Till-  i.ost.Ti()r  i-ont  tilMT.sliortly  iift.T  HiLTinK  tlir  .•onl.^.'iNvs  off 
a  l.ra.u.li  at  rijrl.t  aii-l.-s  (.-allo-l  a  .•oUat.-rah.  or  in  its  .•o.irs..  up 
the  cord  it  nw.v  jiiv  off  s.v.Tal  .-ollafTals.  lli.ir  .i-st  n.at  mm. 
lu.injr  tlu-  fjivv  matt.T  of  the  .•...•.!.  in  wlii.-l.  ti..y  t.Tinn.at.'  I.y 


Kl        1  Dianiam  of  st'ctioi.  of  xi.inal   .■..id,   sl...wiM«   tia.ls.      .All.r   K'.l- 

Mker"        ,  ..sU.|l..r    im-.iian.    an.l    /-.    i.<.st..r..-lat.Tal    .-lumiis :    ,,.-..    .n.ss.Ml 

„yr..T  a  ;  ami  „M..  .linct  pyra.nidal  traots,  /,  .■.-.vl-Uar  l.a.t,  (Affr 
Howell.. 

svnapscs  arouiul  imtv  (vlls.  (".■rtain  of  tlu's.-  may  Ix-  .••■lis  of 
til.'  ant.M-ior  liorn.  Tlu'sc  c.'lls  jriv.'  v\sr  to  tli.-  .■tr.-rn.t  hlxTs. 
wlii.-h  loavc  tlu'  spinal  conl  by  thr  anterior  or  motor  roots  (s,r 
Flit.  41).  Otiifr  collaterals  run  to  int.'rmc.l^ary  ctlls.  which 
then  communicate  with  the  anterior  horn  cells  (Kisi.  V-i). 

The  Xkrvk  ("kntek  ano  1nti;k.mei>iakv  NkihoM'-s.— When 
the  ent.-rinK  nerve  impulse  tnivels  by  a  collateral  to  an  anterior 
horn  cell.  w.>  have  the  simplest  tyi.e  of  reflex  action,  namely,  one 
iuvolvint?  a  receptor,  a  sen.sory  nerve  tiher.  the  post.-rior  r(M>t,  a 
collateral,  the  anterior  horn  cell,  tlu'  anterior  root,  a  motor  nerve 
fiber  and  an  effector  organ.     But  such  a  simple  reflex  seldom 


248 


I'll YSK )!,()« V    P;)K    DKNTAI-    STIDKNTS. 


occurs  in  the  higher  animals.  The  afferciit  i:npulse  when  it  en- 
ters the  cord  is  more  liitely  to  travel  up  the  posterior  columns 
and  then,  as  alreaily  outlined  to  the  cerebrum,  where  it  einls  on 
the  large  i).vramidal  nerve  cells  of  the  gny  matter. 

From  the  pyramidal  cells  spring  the  fibers  of  the  itfinimidul 
Inicts,  which,  as  they  pass  downward  through  the  white  matter  of 
the  cerebrum,  crowd  clo.ser  and  closer  together  until,  by  the  time 
the  basal  ganglia  arc  reached  (optic  tha'amus  on  the  inside, 
and  corpus  striatum  on  the  outside),  they  form  a  narrow  bun- 
dle which  occupies  the  middle  portion  of  the  strip  of  while  mat 
ter  which  lies  between  these  ganglia.  This  whiti'  matter  is 
called  the  iiifiniiil  caitsiih  (Fig.  46),  and  it  is  of  very  great 
clinical  interest  because,  being  in  the  neighborhood  of  a  large 
artery  (branch  of  nnddlc  cerebral),  which  sometimes  bursts  in 
elderly  peo])le,  it  is  apt  to  become  torn  up  by  extiavasated 
blood,  thus  destroying  t!ie  i)yramidal  fibers  and  causing  paraly- 
.sis.  This  is  what  occurs  in  apoitlrxt).  Helow  the  internal  capsule 
the  fibers  run  into  the  crura  cerebri,  then  into  the  pons,  thence 
into  the  ledulla  oblongata,  in  the  front  of  which  thi'v  form  a  dis- 
tinct bulging  called  thi  pijramid ;  hence  their  name  pyramidal 
fibers  (see  Fig.  45). 

In  the  lower  portion  of  the  medulla,  a  most  interesting  thing 
occur-s,  namely,  three-fourths  of  the  fibers  cross  to  the  oppo- 
site vside,  thus  constituting  the  di  cussution  of  the  pi/nimids 
(F"'ig.  44).  These  crossed  fibers  run  down  in  the  lateral  columns 
of  the  spinal  cord  as  the  crossed  pyramidal  tracts.  The  j)yra- 
nddal  fiber.s  which  do  not  cross  in  the  medulla  form  the  direct 
pyramidal  tracts  of  the  cord,  and  they  gradually  cross  in  tin- 
cord  itself.  The  pyramidal  fibers  end  by  synapsis  around  the 
cells  of  the  anterior  horn,  so  that  all  fibers  from  the  cerebrum 
ultimately  cross  to  the  opposite  side  before  they  reach  the  anterior 
horn  cells,  for  which  reason  it  hai)pens  that  a  lesion  involving 
the  pyramidal  trait  anywhere  above  the  decussation,  such  as  the 
luemorrhage  in  the  internal  capsule  above  referred  to.  always 
causes  paralysis  of  the  opposifr  s)d(   of  the  body  (hemiplegia). 

These  facts  regarding  the  course  of  the  pyramidal  fibers  have 
U'cn  ascertained  by  micros<'opic  examination  of  sections  from 


Ki„  4:i -_K,.||..x  an  lluoiml'  Hi"  xpin^'l  '"i'"-  "'  »"''''  •'"  inf'""  >li'"V 
n.-uiono  Hn  blu.O  .-visls  t,..t«...M  ll„.  MlT.nMt  miM  .■n-..,v,>t  ...unm.s.  .It..,,. 
IliiwiU's    l'liysii>lii>,',v.) 


>w^*.'«*'" 


KiK     t^-  —  ''"I"'*"'   " 


f  till'   pyiiiniiiUil    lilH'is 


in  till'  111 


inl : 

ixlul 


/,  tillers  to  nil' 


fiKin 


■lei  i(f  riiinial  iiffvrs 


111.' 


il.iiil    mrl.x    U 


Hill 


.1,  niiiis  w 


liiili  ilo  iiiit  <n 


I  dill' 


■t  pyiiimiiliil  liii'l )  .  1 


III 


til  II 


lllirll  rlii>-' 


111   nil 


illlll;l 


■iissi'il   pyirini 


ili.l    ti:iil  I 


I  Afli  r  lliiwill  I 


7^i'S»>Ci«3h«W6W-*r  ",'■•  yi--^:-': 


«"_  1. 


if  •  - 


i!;l4 


lii 


I    :  i  j-  :i 

if" 


KKKI.KX    ACTUiN. 


24! » 


various  li'vcls  of  tlic  spinal  cord  soiiio  tiiiic  aftt-r  «lfstructiori  of 
tilt'  KolHixlic  area  of  the  ccrchrmn  (sec  p.  270).  Thr  jn  riuiii(i;il 
fil)crs  arc  (it'KCiifratt'd  and  they  occupy  tiic  areas  iiidiijilcd 
in  Fijf.  42.  Since  the  degeneration  occurs  helow  the  ih-structi.m. 
it  is  called  descending  de<reneration.  in  contradistinction  to  as 
cending  deffcneration.  wliich  we  .saw  to  follow  .section  of  the 
posterior  roots  between  their  ganglia  and  the  cord  (see  p.  24tii. 

Tn  Sinn  up,  the  sensory  impulse  on  entering  the  spinal  cord 
by  thi'  posterioi"  root,  by  traversing  a  collateral,  may  take  the 
shortest  possiljle  pathway  to  the  efferent  nerve  cell  of  the  an 
terior  horn,  or  it  may  avoid  this  and  travel  up  the  posterior 
colntnns  of  the  cord  to  tiie  medulla,  thence  by  tlie  Kllet  to  the 
cerebral  cortex  of  the  op|)osite  side,  and  thence  down  tlie  |)yra 
niidal  tracts  to  tlic  anterior  horn  cells.  In  this  long  cerebral 
route  there  are  at  least  three  j)laces  where  the  impulse  must  pa.ss 
by  means  of  a  .syna()sis  from  nervi'  fibers  on  to  nei've  cells,  and 
then  along  the  nerve  filx-rs  arising  from  the.se.  These  three 
places  ar<':  (1)  in  Uie  medulla.  (2)  in  the  cerebral  cnrte.\,  (:<) 
in  the  anterior  horn. 

This  lonji  c' 'rebral  route,  as  it  is  eailed.  is  l)y  no  means  the 
oidy  one  along  which  afferent  impulses  may  travel  to  the  brain. 
Some  may  be  carried  by  collatt  rals  to  certain  cells  of  the  grey 
matter  of  the  cord,  and  from  these  cells  fibers  may  run  up  tiie 
cord  to  the  cerebellum  or  lesser  brain.  These  crnhiUitr  triicis 
are  located  in  the  lateral  columns  of  the  cord  outside  the  crossed 
pyramidal  tracts  (see  Fig.  42).  They  do  not  degenerate  when 
the  j)osterior  roots  are  cut,  but  do  so  after  section  of  the  cord 
itself  (this  distinguishing  them  from  the  fibers  in  the  pasterior 
columns).  The  impulses  which  they  transmit  to  the  cerebellinn 
have  to  do  with  certain  subconj-cious  sensations  concerned  in 
the  maintenance  of  the  tone  of  the  muscles.  There  are  also 
ccrtjiin  pathways  in  the  white  nnitter  of  the  cord  which  trans- 
mit desvcnding  imi)ulses  from  the  cerebellum. 

The  main  bundles  of  ascending  and  descending  fibers  in  the 
spiui'l  cord  are  charteii  in  Fig.  42.  which  should  be  carefully 
studied. 

TiiK    Kkfehi;nt    Fibek,    ok    .\ki  KONt;. — As  already  explained 


f^M^-^.-m 


250 


I'IIYSIOl.«M)Y    FOK    DKNTAI-    STIOENTS. 


I     ' 


tlic  coll  of  this  iHMinm.'  is  located  in  the  anterior  horn  of  kitv 
matter  of  the  conl.  These  anterior  horn  cells  are  (Ustinnnisheii 
from  the  other  nerve  cells  of  th.'  K'vy  matter  by  their  lar>.'e  si/e 
anil  anRular  shape,  and  they  liecome  jrreatly  increased  in  num- 
ber in  the  |)ortions  of  the  cord  from  which  the  nerves  K'»""'>-'  <" 
tile  extremities  oi-ifjinate.  The  fibers  spriinrinn  from  tiiein  pass 
out  in  the  anterior  roots.  If  th lis  are  destroy<-d  or  the  an- 
terior r(M)ts  cut,  defeneration  cccurs  below  the  lesion,  and  |)ara- 
lysis  of  the  etfector  organs  (muscles)  to  which  they  run  results, 
but  this  i)aralysis  is  very  sli^lit  in  decree  unless  the  lesion  af- 
fects s<'veral  roots,  or  the  cells  of  several  adjacent  levels  of  the 
cord.  The  rea.son  for  this  is  that  the  nerve  colls  of  one  level  of 
the  cord  only  partially  supply  a  given  muscle  or  group  of  mus- 
cles with  nerve  fibers,  thus  showing  that  even  the  small  nmscles 
receive  their  nerve  fibers  from  several  ad.jacent  levels  of 
the  cord.  The  anterior  horn  cells  sometimes  become  tlcstroycd 
by  disease,  namely,  in  infantile  i)aralysis  (poliomyelitis  anter- 
ior).    The  resulting  paralysis  is  never  recovered  from. 

Types  of  Reflexes.— Having  traced  the  paths  through  whi<li 
reflexes  occur  in  the  higher  animals,  we  may  now  jiroceed  to 
consider  certain  typical  forms  of  retlex  action  and  the  eondi- 
lions  which  may  cause  them  to  become  altered.     We  nuist  fi:"st 
of  all  confine  our  attention  to  the  characteristic  reflexes  of  the 
so-cal'fd  .si>liifil  (nii)titil,  for  it  is  only  after  we  have  done  .so  that 
it  will  be  itt)ssii)le  for  us  to  determine  what  influence  the  briin 
has  in  modifying  the  spinal  refl.  xes.     Tiie  spinal  animal   (dog, 
for  example)  is  prepared  l.y  cutting  across  the  spinal  cord  some- 
where below  the  origin  of  the  phnnic  nerves.     After  the  immc- 
di.ite   eti'ects   of   the    operation    have    been    r.-coverd   from,   the 
regions  of  the  animaKs  body,  lying  lu'low  the  level  of  the  sec- 
tion of  the  cord,  suffer  from  a   i-omlition   called  spnni  shock. 
All  reflex  nu)vements  are  absent,  the  sphincters  ai     paralyzed  so 
that  incontinence  of  urine  and  fa-ces  exists,  and   various  "tro- 
phic" or  nutritive  changes  occur  in  the  skiii    (ab^.rsses  form, 
hair  falls  out,  etc.).     After  some  lime,  the  length  of  which  de- 
pends on  the  po.sition  of  the  aiiiinal  in  the  animal  ^eole.  the 
sphincters  regain  their  tone  and  the  reflexes  gradually  reappear 


ItKlM-KX   ACTION. 


251 


i„  til.'  i.nnilyzcl  n^um.  thv  tirst  to  .1..  s..  U'Um:  \hv  i-rofTtiv.- 
rttl<'X.-s,  of  whicli  th.'  fluioii  nfhr  is  tlir  tvi.c 

Thr  rt.-xion  n-H.-x  is  .licil.il  l.y  iiii.v  stiiimlns  win.li  woul.i  .-inisr 
,,,,i„  i„  an  animal  .•ai-abl,-  -f  \W\\l^^^.  Surh  slin.uii  an-  rMvd 
lux-uoiis  an.l  tlic  ivfl.'X  ivspons..  is  ahvavs  o(  s.i.-h  a  nat.iiv- 
usuallv  H.xion— as  to  caus-  llw  injuiv.l  part  to  1h-  r.-niov.,! 
from  fi.rtluT  .lannmr.  Tlu'  nturn  of  tl..-  H.-xion  r.-flrx  is  s.Mm 
r„ll,mv.l  l)v  that  of  til.  kix,  ././•/..  which  is  .'licitr.l  hy  taj.i.n.t; 
th.-. patellar  t.Mi.lon  aft.r  putting  it  on  ti...  stnt.-h  l.y  passivly 
iM.n.linK  tlu'  kn.-.-  joint.  Somr^hat  lat.-r  in  many  annm.ls  ^...^' . 
,1,,^;)  //„  svrolrh  nfl<.r  ai-lu-ars.  so-call.-.l  l«-.'«us..  it  consists  ,.t 
a  scratcl.ii.p  movmcnt  of  th.-  hin.l  l.-«  in  n-sponsc  to  mechanical 
irritation  of  the  flank  of  the  aniu.ii:     It  is  a  retlex  of  very  K"eat 

i.iteivst  iH'cause   it   illustrates  to  what  a  remarkable  d. «! the 

.spinal  cor,!,  unaided  hy  the  brain,  is  capable  of  brinnuiK  about 
eomplicated  and  i.nrposeful  eo-onrmated  movement.  I-ater  still, 
in  the  lower  animals.  practicall.N  all  the  reflex  movements  which 
a  normal  animal  exhibits  may  ivippeiir. 

When  the  con!  becomes  severed  in  man.  as  by  spinal  fracture, 
spinal    shock    is    extremely  profound,  and  in  order  to  keei.  the 
pati.nl  alive  -tvat  car.'  must  !«■  tak.  n,  ..n  a.-count  of  the  mcon- 
tinonco  of  uriii.-.  to  pr.veut  inf.'ction  of  the  bla.l.ler  an.l  ki.lii.'.ys 
an.l  to  prot.'ct  th.>  skin  fr..tn  ulcration  (be.l  soros).     Kvcn  in 
such  cases,  howev.-r,  many  of  the  reflex.-s  r.'cov.  r  in  the  para- 
lyzed regions,  but  the  recovery  is  slow  and  th."  limbs  invariably 
atrophv.    It  is  particularly  important  to  note  that  th.-  time  of  re- 
app.-aranc-  of  th.-  reflexes  b.-ars  a  relationship  to  th.-  .IcKreo  of 
d.-velopment  ..f  the  c.-r.-bral  hemisphen-s.  thus  r.-iul.-riiifj  it  .-vi- 
d.-nt  that  spinal  shock  is  due  to  a  br.-ak  in  the  n.-rv.-  paths  which 
lead  to  ami  from  the  brain.     Th.-  hijjher  the  animal,  th.-  moiv 
fr.-.!U.-ntlv  do  all  r.-flex  acts  involve  a  .-er.-bral  path  inst.-a.l  of 
takinji  tli.-  short  cuts  available  through  the  collat.-rals   (see  i-. 
24:^.     Knim  usaire.  as  it  were,  the  c.-r.-bral  paths  b.-come  so  w.-ll 
dev.-l..p.-.l  that  wh.-n  th.-y  an-  sudd.-nly  s.-v.'r.-d.  th.-  n-fl.x  action 
b.-.-..m.-s    impos,sibl.-    until    the    ent.-ring    attVr.-nt    impuls.-    has 
learned  to  use  th.-  hitherto  unus.-d  short  cuts  available  through 
collaterals.     When  completely  .-ecoveivd  from  spinal  shock,  an 


rif» 


•>.v> 


UYSIdltKlY    KitH    DKNTAI.    STIOKNTS. 


aiiiiiiiil.  May  a  dotr.  in  so  far  as  voluntary  inovfin.-iit  is  i-oii- 
(-.•nuMl.  is  .•ntir.lv  paraly/.'.!  in  all  |)ortii)ns  of  tho  »»o<ly  l»<-lo\v 
Ihf  l.'Vfl  of  till-  s.'<-ti()n  of  th.-  .-onl.  It  cannot  voluntarily  move 
the  iitr.'ctc.l  l)arts.  it  cannot  walk,  it  fc.ls  no  |>aiM  or  any  other 
sensation  hclow  tin-  icsi.Mi.  ami  y.i  wh.'U  approj.riatcly  stiniii- 
iat.'.l.  the  |taraly/.'.l  limbs  nniy  nil.  xly  undergo  various,  often 
very  coniplicate.1  inovemenf^ 

The  Essential  Characteriitics  of  Reflex  Action.— As  sfu.li.<l 
on  a  pcrf.'ctly  recoven-.l  spinal  .loj.'  th"'!**'  «'"''  •"<  follows: 

1.  For  H  certain  interval  after  applyinjr  the  stimulus  tli.r.' 
is  no  respon.s.',  the  .hiration  of  this  "latent  peri.Ml"  <l.'])en<liiii: 
partly  on  the  nature  of  th.'  r.H.'X  (short  in  the  prot.-ctive  re- 
tl.-x.'s.  lonjr  in  the  scratch  r.«flex  i  and  partly  on  the  strength  of 
the  stimulus. 

2.  The  response  may  |).-rsist  for  some  time  after  tlie  stimulus 

is  renu)v.'.l  (aft.r  rcspons."'). 

:{.  The  decree  of  the  response  is  roujfldy  proikortional  to  the 
stn-ngth  of  the  stimidus.  excei)t  in  c.-rtain  of  the  prot.-ctive  re- 
flexes, such  a.s  th.-  con.junctival.  whi.'h  c.)nsists  in  th.-  chisinjr  of 
the  ey.lids  when  anything  touches  the  eye. 

4.  Tlu-  response  is  often  rhythmical  in  character,  ev.-n  though 
till-  stimulus  1).-  continuously  appli.-d.  This  is  w.-ll  s.-en  in  the 
.scratch  reflex. 

5.  There  an-  certain  ways,  apart  from  an  alt.-ration  in  the 
stimulus,  by  which  we  may  cause  a  r.Hex  movcm.-nt  to  become 
increase.!  or  decreas.-d.  Thus,  taking  the  flexion  reflex  as  an 
examph',  the  flexion  nuiy  b."  flinuiiishid :  (1)  by  stinuilatiiiR 
some  other  reflex  movcm.-nt  which  involves  the  same  muscles, 
but  which  is  antaKonistic  to  flexion,  e.g..  by  stimulating  the 
.)l)positc  limb  an.l  causing  tlu-  so-called  crossed  ext.-nsion  refl.-x; 
(2)  by  causing  stroufr  atTen-nt  impulses  to  i»ass  through  other 
levels' of  the  spinal  cord,  e.  g..  pinching  the  tail.  A  similar 
•'ititrrfirriin  "  is  well  illustrat.-.l  in  the  case  of  man  by  stimulat- 
ing th.-  fiftli  n.-rve  by  firm  pr.-ssur.-  on  tlu-  upi).-r  lip  at  a  time 
when  then-  is  an  inclination  to  sne.-/e.  The  sne.'/.ing,  which  is 
a  reflex  due  to  irritation  of  th.-  mucosa  of  the  nose,  can  usually 
be  prevented.     Expres.sing  this  i)henomenou  of  reflex  interfer- 


KKKI.l  \    ACTION.  -■'■' 

,.,„,,  i„  populnr  lanjrui.K'.'.  w  n,av  say  that  wli.i,  ih.-  att.nli..,, 
„|-  a  >^-vuu-u\  ..f  th-  .-onl.  or  its  .kUuhwu  it.  tli-  Lnui,  is  t;,k.i, 
„p  hv  somr  ..th.T  stiimili.M.  a  .vflx  aliva.l.v  in  art...,,.  ..r  aLui.t 
to  a.-t.  is  .l..|.iv,vs...|.  I'ain.  sii.-l.  f..r  .xaini.lr  as  t.M.tharl,..,  may 
lik.'wis.-  !..•  I.-SS.M.MI  l.v  applyiiilf  rount.T  irritation  sii-h  as  a 
l.list.T  to  somr  n.itfliborii.K  skin  an-a.  -  :f.  I'.y  m.-ans  of  .vrtan, 
,ln.«s  knou  n  as  anrstla-ti.-s.  wl.i.-h  .l.-l.'''"'''*  '>"'  ••x.-ital.il.ty  ol  tlu. 
iirrv.'  '•.'Us.     (4)   lU-  fatiK'iir. 

Thr    -H.-x   inovHa.M.t    may    hv   ' >is,,l:    H)    L;.    a|.pl>  imr  a 

s..-o,ul  s,  Mulus  to  son,.-  oth.-r  a  ■  ^  ■■'  ^i-ii.  of  tl..  samr  liu.-l  l-s^ 
o.  hv  ai.i»lvi>.u'  ..lr.-tri<-Hl  stimuL  .....  !  >■•  ^--r'tml  .;n.l  <'t  '•'"• 
„f  lis  sensory  nrrvs;  (U  >  Uv  n..  n  :.  v  ,■  ,  s.-ita'.ihty  ol  th. 
,H.,-Nr  ....nt.Ts  by  n-rtain  .Irnjrs.  sr.  .  .^  >t  rv.,;M.nr ;  Ct  i  hy  t.rst 
„r  „11  ..Musinjr  th.  inov.-inrnt  to  .lis,.,,,..-.  . ,  M:..UKh  th..  stnnuh.tmn 

.•ausinn   it    is  maintain.Ml.   In    .x.-itinw  son..-   ..tn.T    |.ait    ..I    th.- 
ho,ly   (s..,.  ahov.-i.     Wh.^n  th..  r..f1..x  n-ai.iH.ars  it   is  much  mon- 
prononni'f.l  tlian  forna-rly. 

Muscular  Tone  and  Reciprocal  Action  of  Muscles.    Ilavm^r 
.l,,,rn.Ml  son,.,  of  th..   ^..n.fal  .■ha,.a.-..risti,-s  ..f  th-  n-H-.x   n.ov..- 
„„.„ts   w  m.tv  i,ow  p.-oc...Ml  to  in.iui....  into  th..  m.th...l  I.n  whu-h 

th..  spinal  ...nl  is  ..nahl.-.l.  hy  its..lf.  so  t..  .lir...-t  th.-  alT..r.M.t  „n- 
.,„ls..s  \vhi..ii  ..nt.-r  it,  that   ti,..  n.-rv..  ....lis  of  th.-  ant..i-,or  h..rn 

,'ns..har>r..    siiitahh.    iinpuls.  s   f.   brin^'   ahont    su.-h    .•.m,pli..at...l 
m„v..,„..nts  as  I.mn      jnst  h....n  .l.-s.-rilH-.i.     Wh.-n  a  motor  n.-rv 

or  an  ant.-rior  spi„„i  n..)t  is  stimulat.-.i.  iIh-  mus.-h-s  Nviu.-h  ..mi- 
ti-a.-t  ar.-  imt  j;i-owp.-.l  in  su.-li  a  way  as  to  .-aus,-  any  pi,rpos.-l„l 
,„.  ,.o.oi-.li„at.-.l  in..x  -u.-nt.  C.nti.a.-tors.  ..xt..ns..i-s.  a.i.lu.-t..i-s 
a„a  ahdm-tors  ar.-  Mint-  lik..|:  all  t..  .-ontra.-t  at  on.-.-  an.l  hy 
thus  (.|.posin«  oiu-  aimth.r  to  ..tf'.-.-t  n..  .l.tinit.-  m..v..m..nt.  \N  h..., 
sm-h  stimulation  is  .-xf-nsiv.-  (.-.jr.,  involv.-s  a  .-onsi.l.-rahl.-  num- 
l„.r  of  motor  tib..rs),  it  is  .-oinmm,  to  Hn.l  that  th..  .•xt..ns.,r 
„mse-U-s  pi-..dominat.-  ov.r  th.  oth.-rs.  so  that  th.-  limb  b...-o.n.-« 
.•xtind.-.l.  Such  is  th.  cas,.  wh.-n  some  p.»isonous  siibstanc- 
c-aus.-s  irritation  of  th.-  n.-rv.-  .-.-nt.-i-s  in  th.-  spinal  cor.l. 

To  i-aus.^  a  i-o-onlinat..!  niov.-m.-nt  it  is  n.-.-.-ssary  that  oii.- 
sjrmip  of  mu8<-!.-«  shonl.l  b.-.-om;-  ...lax.-.l  whilst  th.-ir  antap,nistic 
group  is  uiulerKoiuK  contraction.    Now,  it  might  at  first  sight  1... 


E:m  . 


2.'.4 


l>nYSI<>I><»nY    FOR    HKNTAI.    STinEXTS. 


r: 


It 


imagined  that  this  n'laxatioii  is  iiuTcly  a  passive  act.  that  is  to 
say.  that  the  uiu-ontractiiiji  Kroiip  of  iiiusch-s  (h)  iiotiiiiin  iiioiv 
tl-.aii  rcinair  .iiii«'»<'<'"t  'i'"!  l>*'rinit  tht'insflvcs  to  Ik-  stretohcd. 
Hut  such  is  not  the  case ;  on  the  contrary,  they  become  aetively 
extended.  This  they  are  enaWed  to  do  because  of  the  fact  that, 
even  when  api)arently  rebixed,  a  niuseh'  is  really  not  so.  but 
exists  in  a  eondition  called  touf,  that  is.  in  a  sliglitly  eontraet.Ml 
state.  This  tone  becomes  greatly  diminished  during  sleep,  and  it 
can  be  caused  almo.st  to  disappear  by  deep  anesthesia.  It  is  for 
this  purpose,  as  well  as  to  abolisii  pain,  that  anesthetics  are 
administered  before  attempting  to  reduce  a  dislocation. 

Tone  is  maintained  by  the  nerve  cells  of  the  anterior  horn  ot 
the  spinal  cord.  When  therefore  an  aflfereiit  impulse  brings 
about  flexion  at  the  knee  joint,  it  does  so  by  exercising  two 
diametrically  opposite  influences  on  the  anterior  horn  cells:  it 
stimulates  thos«-  which  preside  over  the  flexor  nmsdes  and  (h- 
pnssrs  the  tonic  influence  of  those  supplying  the  extensors. 
This  tone-depres,sing  action  recalls  the  inhibitory  influence  which, 
the  vagus  nerve  exercises  over  the  heart  beat  (see  p.  185).  and 
since  it  always  occurs  along  witli  a  contraction  of  antagonistic 
nniscles  it  is  callcf/  ncijirocil  inhibilion.  Certain  jmisons.  par- 
ticularly strychiiine  and  tetanus  toxin,  cause  this  reciprocal 
action  to  break  down  so  that  all  the  nniscles  around  a  joint  con- 
tract at  the  .same  time  and  phmIucc  an  extension.  Tetai'.us 
toxin  is  the  poison  |»roduced  in  the  blood  by  the  tetanus  bacillus, 
and  its  interference  with  the  reciprocal  inhibition  of  the  muscles 
of  the  lower  jaw  causes  lockjaw. 

Symptoms  Due  to  Lesions  Affecting  the  Reflexes.— From 
what  we  have  learned  regarding  the  functions  of  the  spinal 
cord,  it  is  easy  for  us  to  explain  the  following  symptoms  an<l 
conditions  re.sidting  from  pathological  destruction  or  stimula- 
tion of  various  parts  of  it : 

1.  In  destruction  of  the  <'ontinuity  of  the  afferent  or  ef!"erent 
fibei-s  of  the  reflex  arc.  the  reflexes  are  absent.  This  occurs  in 
chronic  inflanunation  of  fh  ■  nerves  (muritis)  and  in  the  disease 
called  hivnmoUn-  iitn.riu.  m  wlii<'h  the  lesion  consists  of  a  de- 
structive pathological  process  involving  the  postei'ior  eohunns 


KEFI-KX    ACTION. 


255 


of  the  si)iiial   cor.l.     Ouv  of  tlu'  Hist    symptoms  of   locomotor 
ataxia  is  a))snu-e  of  tlu-  k.u'.'  j.-rk.  whirl.,  it  will  1m-  n-m.-mh.-iv.l. 
is  elicited  by  tapping  the  patellar  teiulon  aft.-r  putting  it  i>as- 
sively  on  thi-  stretch,  either  by  sitting  with  th.-  fe.'t  swinging  on 
the  edge  of  a  table,  or  by  crossing  one  knee  over  ilie  other.   I'aiiis, 
called  crises,  are  also  usiud  in  various  |)arts  of  the  bo«ly.     Later 
svmptoins  are  inability  to  staii.l  without  falling  when  tiie  ey.-s 
are  shut,  inco-oi-dinated  walking,  in  which  the  foot  is  lifted  too 
higli  and  is  brought  down  to  the  ground  again  too  violently,  loss 
of  .sensation  of  the  .skin  of  the  foot  and  leg.  and  changes  in  th.- 
pupillarv  reflexes  of  tiie  eye   (s.>e  p.  2H4).     The  .ioints  also  be- 
come swollen  and   the  articular  surfaces   roughened   so  that  a 
grating  sensation  is  experienced  when  the  joint  is  bent   (Char- 
cofs   joint).     The  condition  gradually  gets  worse,  so  that  the 
patient  becomes  bedridden.     Death  is  usually  due  to  comi)rica- 

tions. 

2.  Destruction  of  the  anterior  horn  cells  not  only  causes 
absence  of  ivHcx  action,  but  is  followed  by  marked  atrophy  of 
the  atVected  muscles.  It  has  been  supposed  that  this  i)oints  to 
a  so-called  trophic  influence  of  these  nerve  cells,  that  is  to  .say. 
a  i)ower  of  influencing  nutrition.  Such  changes  occur  in  infan 
tile  paralysis  (poliomyelitis  anterior) 

:{.  Stimulation  of  the  above  HImm-s  may  cause  exaggeration  of 
the  reflexes,  as  in  the  earlier  irritative  stages  of  neuritis,  in 
tumors  pressing  on  the  nerve  roots,  or  when  the  membranes  of 
the  cord  become  inflamed,  as  in  meningitis. 

4.  Kemoval  of  impulses  coming  from  the  cerebrum  by  way  ol 
the  pyramidal  tracts  causes  exaggi-rated  reflexes.  Such  occur 
in  paralysis  of  both  sides  of  the  bo.ly  in  j.arapleiria.  and  on  one 
side,  the  ))araly/ed.  in  hemiplegia. 

In  a  paraplegic  patient  the  weak.'st  stimulus  applleil  to  the 
skill  of  the  paralyzed  portion  of  the  bodv  will  cidl  forth  a  wide- 
spread aud  much  exaggerated  lu-flex  contraction. 


CIIAI'TKH  XXVir. 

TIIH  NKUVOls  SYSTKM  (Coiifd). 

The  Brain  Stem  and  the  Cranial  Nerves. 

The  Brain  Stem. — The  mtMlullii.  the  |)()ns  varolii,  iiiui  IIh-  inid- 
liniiii  (  Kisr.s.  4.")  and  4()),  (•oiiii)osc  tlic  brain  stem,  wliicli  is  n-aliy 
an  ui)\vanl  extension  of  the  nwy  matter,  ami  of  certain  of  the 
columns  of  the  spinal  cord,  into  the  base  of  the  brain  with  special 
nerve  eenler.s  and  especially  larjrc  bundles  of  intei-eonnectinfr 
nerve  fibers  superadded.  It  is  becau.sc  of  the  crossing;  in  various 
directioUK  of  these  bundles  of  tibers  that  the  structure  of  the 
medulla,  pons  and  nii'sencephalou  is  .so  ditTicult  to  und-M'stand. 
The  prey  matter,  as  in  the  spinal  cord,  lies  deeply  and  the  tibers 
superficially.  <  ►f  the  latter,  the  |)yramids  and  fillet,  already  de- 
scribed, are  the  most  im|)ortaiit.  and  their  direction  is  loniji- 
tudinal.  The  most  i)iominent  of  the  eomiectinp  or  coinmisural 
nerve  bundles  ai'e  the  upper,  iiiichile  and  lower  i>((lnntlis  of  flit 
CI  n  hilhiDi.  or  snuill  brain,  which,  it  will  lie  remembi-red.  lii's 
over  anil  at  the  side  of  the  pons  .irolii  and  niidbram.  The 
hr.vT  peduneh's  spring'  from  tlie  mh  dnila  and  etmnect  the  spinal 
cord  with  the  c<  iebelhim.  They  form  the  lowet  edges  of  the 
fourth  ventricle  Th»  middle  peduncles  I'uter  the  sids  of  the 
pons  iri  which  they  cross  at  ri^rht  anjjles  with  the  pyramidal 
tibirs  I  p.  24Si.  Tln^y  connect  the  ..•rebellum  of  one  side  with 
the  ci  I'ebrum  of  the  oj)|)osite  side.  The  superior  peduncles  .jo:n 
the  ene.phalon  just  under  the  jtosterior  corpora  quadrijrennna. 
and  'he  fibers  eomiiosintr  them  di cussate  to  the  oth.'i'  side  to  be- 
come eoiniicted  with  certain  of  tb--  so-called  basal  u'anfrlia. 

The  hiisal  niiiiiilid  are  the  o|  he  Ihalanuis  and  the  corpora  stri- 
ata, tni;  larye  collections  of  nerve  cells  |)riitrudintr  into  the  third 
and  lateial  ventricles  of  the  brain  and  havinjr  the  internal  capsule 
between  them  see  |i.  24is  J .  Tile  nerve  cells  eomposiu'T  these 
f.rangli;i  receive  impulses  from  tiei've  fibers  arriving  at  lliem  both 

2Sm 


TlIK    BKAIN    STKM. 


::.)( 


from  l.rlow  (cDiirmjr  fntiii  the  spmal  cord)  or  from  abov.-  (coni- 
iim  from  til."  (•(•rcbrmn).  Tli.-y  tli.-ii  transmit  tlu'sc  impnls.s 
aloti"  tht'ir  own  ii.rvf  fibers,  wbidi  may   run  to  various  otlicr 


Via     (.'.    -  rmhi     .ispiil    of    hiiMKin    luiiiii.       Iti    tln'    .'fiit.-v    Inu' 
„|,u;.nls    HI-    s.-,-n    a    s...-lion    .-f    th.-    uppiT    .'M.!    ,.(    th.-    spin;,!    coni.    :.t..l 
.u.-ihillM   .ilil.iiiy-iitii    n»l,    with   .■.■iiHin   <>{  itu-   tiMiii^i 

1„    f,,,nt    of   Uiis   is   \h,    p..nw    <;.).    witii    th.>   law   lifHi    ...iv.-   ..risit.K    ffn.H 
;,,..!   ill.'  iiiiil.ll.-  pedun.l..«  ..r  ill.'  v.-i,u.-\lum   iM.   r<.l}    imumuk   mt..  it.-  '■•■> 

l„.|liirn    1.1'       Til.    r.mtwl.T  Im.iM.'s  ;,i,i.i,''^    to  the  \ixux  i.iv   ih \'«v:<     i'l' 

memina  ir,,i     i.,  •!,     si<l.-s  of  wl.i,l,  ..i.    tli-  rrufii  .•.■ivl.ri   ...,.1  tl..'  (.nifii.« 
ll„-    lliii.l    :,n,l    fourtli    m-rvt-x       Th.'   ..pti.     .,r,.l    ,.lf;irt..i  y    ti.i\.s    :uv    in    fn.^ 
Tlr.     iiriil.-i     xnv(M-i-s    ..!'    ili..    r.i.l.nim     KM     ;iM<i    .■.■r>-l,..|  iUM.     i  .1  (    .•otislHM 
tl„     .•.■i,i;,in.l..|    ..I-  tlu    ,li:ivvinK       ,  r,,.m   a    p: .  p.iiMti...     !■>    r     M     Spiirn.-v. . 


2."^ 


fIIYM(»lAX;V    F>il{    DiATAI.    ^TIHENTS. 


\tiirU  o\'  ^^■^    l)raiii.     Th.   optic  flialanHK,  as  its  iiaiiic  signifit's,  ts 
'•itiiiiati'l\    iisKooiatiil  vvitli   the  opti«'  iktvps. 

Allotllcr  iiaportailt  CKilci-tloii  of  nerve  eells  oeeiU'S  ill  the 
ii>riK>rii  ifiKtfiriffi  "H»(i.  Thesi-  ixnit  as  t'onr  uuiKled  swellirms. 
two  oil  litller  side,  just  where  tim-  s«|*eri(ir  jietiiiiielcs  df  the  cere- 
liellum  come  tofft'ther  Their  nerve  eellv  wrve  a->  distrt^watiiitf 
centers  for  visual  and  auditors  intfut^se-".^  cjirried  T(»  them  throu;;!' 
ti-aets  of   nerve   fibers     oinieetMi   with    ihc   optic   and   auditory 


KlS.  4ti — Vertical  trimsverKt  stM-tmn  iif  liumaii  hniin  Below  is  n  soctioii 
(if  tin-  imiis  I /'I  .shiiwiiiB  the  lilitM!<  which  luiiiu-it  Ihi-  liniin  stt-m  ami  letf- 
hiuiii  railiutiiiK  up  ihrouKh  thf  Intel  iial  caimuh'  (l(').  which  Ih  liouiul.il 
in.-siallv  hy  thf  optic  thalmus  (T^.  ;iiii  laterally  by  the  corpus  stiiatuni  (/-). 
Till-  thiril  (Ill-V)  and  lateral  ventricles  i  LV )  i)t  the  brain  are  seen  in  the 
ciiiiii  (hlaik)  The  thickness  of  the  Krev  matter  ami  the  infoliiiiiK  of  lie' 
surfaees,  as  eonvoUitions.  should  )»■  noted.  i  I'"rom  a  preparation  hy  I'  M 
Spuriiej , ) 


Mifvs.     Tile  corpora  i|Uadri^eniina  are  usually  iiioi-e  developed 
in  the  hraiii  of  the  lower  animals  than  in  that  of  man. 

The   Cranial  Nerves.— On   aeeount    of   the   iMtrodiietioii    of 
the  new  struetures  described  above  theiv  is  no  regularity  in  the 


TIIK   CRAMAI.   NKRVES. 


259 


iinangi'iiicnt  of  tlic  {in-y  niattcr  in  tlic  bmiii  stem  .is  tli.'iv  is  in 
tilt'  conl.  Instead  of  forming  liorns.  tlic  ^'n-y  iiiiitlcr  is  .sc.it- 
ti'U'd  ill  colonics  or  nnclci,  many  of  wliicli  arc  centers  for 
tlic.  Hhcrs  of  tlic  cranial  nerves.  Sonic  of  these  filters  arc.  of 
course,  afferent  and  sonic  ctfercnt.  Since  many  of  the  cranial 
nerves  are  connected  with  the  no.se.  mouth  and  teeth,  it  is  im- 
jiortant  for  us  to  learn  soniethinji  conccrniiiit  the  location  of 
their  centers  and  the  jjeneral  function  of  the  nerves.  There  are 
twelve  pairs  of  cranial  nerves,  and  the  last  ten  of  these  orisrinate 
from  the  sfrey  matter  of  the  medulla,  pons  or  midhrain.  The 
followin(r  list  indicates  the  fifK'i'al  functions  of  the  nervc> : 


1.  Olfactory. 
]>.  Opuc. 

■;.  <  >nulo  m«H»r. 

4.  TTcwchl   .»r. 
»;.   AfbdHe»*n8. 

.'i.  Trigeminal. 
7    Kacial. 

5.  Auilitor\'. 


!t,  (i1o980-pharyn- 
gpal. 


Iti.  Vagus. 


11.   Spitial  iiceessory. 


nerve  of  smell, 
nerve  of  sight. 

nerves    to    the    mii.s- 
cles  of  the  eyeball 

sensory   nerve  of 

face, 
main  motor  nerve  of 

face  muscles, 
nerve  of  hearing  and 

of    semicircular 

canals, 
motor  nerve  of  phar- 

yn.\.  sensory  nerv^* 

of  taste, 
efferent  and  aS'-rcni 

nerve     to      -•rimis 

viscera 
mainly    blends    with 

vagus 


motor    nerve    for 
tongue  muscles 


arises  from  fore- 
brain 

arises  from  fore 
brain. 

arise  from  midbrain. 

arises  mainly  in 

pons. 
arises    in    pons    a'ul 

medulla. 
arises  in  pons 


arises    mainly    in 
mMliiIla. 

arise*    in   rowJulla. 


arises  with  vagua 
except  spinal  por 
tton,  whicti  extends 
down  into  spinal 
cord 

arises    in   medulla 


12.  Hypoglossal. 

It  is  imi)ort:iiit  to  note  that,  like  the  spinal  nerves    many  of 
the  cranial  nervi-s  arc  compiscd  of  two  roots,  motor  and  !k-nsory. 


260 


PIIYfsntl-nCY    POK    OENTAl,   STTPKNTS. 


.■ach  liaviiip  its  own  center.     This  fact  justitics  tlic  statement 
whieii  we  luive  aliva.ly  mad.-  that  the  brain  stem  is  really  an  up- 
ward prolongation  of  the  spinal  eord.  and  just  as  we  saw  that 
eaeh  posterior  root  of  the  spinal  eord  is  eharaeteri/.ed  by  pos- 
sessinK  a  ganglion,  so  also  is  there  a  gitnglutn   in   Ihr  sensory 
divisions  of  thi  cranial  nrrns.    This  ganglion,  however,  is  often 
diffieult  to  tiud.     The  nerve  cells  which  compose  it  unite  with 
tlu'  fibers  of  tlu'  sensory  root  by  a  T-shaped  junetion.  and  the 
fibers  terminate   by  .synapsis  around   th.'   cells  of  th.'   sensory 
nuclei.    The  ganglion  of  the  fifth  nerve  is  the  (lasserian.    Those 
for  the  eighth  are  the  ganglia  found  in  the  cochlea  and  internal 
auditorv  meatus  (Scarpa's  ganglion).    The  ganglia  of  the  ninth 
and  tenth  nerves  are  situated  along  the  course  of  the  nerves. 
The  approximate  position  of  the  various  ganglia  will  be  best 
learned  by  consultation  of  the  accompanying  diagram  (Fig.  47). 
In  the  brain  stem  there  are  three  sensoru  or  affrrent  nuclei,  a 
l(.ng.  combined  one  for  the  ninth,  tenth  and  eleventh  nerves,  ex- 
ten.ling  practically  from  the  upper  to  the  lower  limits  of  the 
m.-dulla,  one  for  the  eighth  in  the  center  of  the  pons,  and  a 
very  long  one  for  the  fifth,  extending  from  near  the  upi)er  limit 
of  "the  pons  down  into  the  siiiiial  cord.     The  motar  or  iff<rcnt 
uueUi  for  the  third,  fourth,  sixth  and  twelfth  nerves  are  com- 
posed of  cells  shai)ed  like  those  of  the  anterior  horn  of  the  spinal 
cord.     They  lie   near  the   middle  line  and  extend   throughout 
the  whole  length  of  medulla  and  ixms.    The  motor  nuclei  of  the 
fifth,  seventh,  ninth,  tenth  and  eh'veiith  lie  outsid.'  the  above. 

It  is  important  that  the  following  functions  of  thrs,   n,n-fs  b- 
studied  by  dental  .students: 

TiiF  TiiiKi)  Nkkvk.— The  third  nerve  controls:  (D  the  mus- 
cles of  accomnuxlation  inside  the  .-ye;  (2)  all  of  those  which 
are  attach..l  to  the  uutsi.le  (.f  the  eyeball,  except  the  mus.-l.. 
which  moves  it  out  (ext.-rnal  rectus),  and  the  one  which  rotat.-s 
it  down  and  out  (the  sui)erior  obliiiue)  :  and  (:M  th.'  elevator 
nuLsch-  of  the  evelids  ( levator  palpebra-).  When  the  third  nerve 
is  paralvzed,  tlie  svinptoius  aiv  therefore:  (1)  drooping  of  the 
,  velid  (ptosis)  so  that  the  chin  is  tilt,  d  upward  when  the  pa- 
iicnt  looks  at  anything;  (2)  inability  to  see  clearly  unless  when 


FiK  47.  liiiiKnmi  o.  tti.  dtusal  :is|»Tt  i.f  t-,-.  mtfiiiilu  iitnl  puiis  vhtiU'.fr? 
thf  Moor  oi  111.'  fouitli  \<-iitii.'i-  Willi  Uu-  nutlfi  of  ■»riKiii  a  Itu-  .  r.ir-i.i 
iiiivis.  I  AfttT  Slnri  iriK'ioM  I  ">»-  Hfiinory  iiu<-!«*i  .trv  <-o'ort<l  I<<1  i'liil  ;»« 
minib»TH(i  on  Ihc  l<fi  ol  ih»  .iiani  .ai.  Ihf  irolor.  liliM-  ami  iiiiiiil"  nil  oti  l»ii 
riKht.  Th*-  p.  liunrU -s  of  Ihr  ^  r.-l~  Uim  -  .s  i  supiTioi  ».  .U  imiil«tli».  iiii-  ' 
are  shown  cui  m  p.ss.  CI)  .(•rs^-  .iiiiili  infoiiii.i.  'I'll.-  .ilHivi'  iiml.'i  sir.  >( 
roUfHi-  pi-fHt'iil   on   hold   snit- 


THE  IKANlAli   NKRVES. 


2(il 


objcus  arc  at  a  .listance  (louK  HJght)  ;  (3)  sMuiut  of  tho  .-.w  s. 
that  it  is  aircctetl  outwanl  and  downward. 

Sud.  a  paralysis  of  tlu-  eye  is  soinrtin-rs  a.-.-om,.an..d    -y  . 
partial  h.  ,ni,»l..gia  (sv-  p.  271)  of  tlu-  opi.os.t.  s.do  ot    1,..  l.o.  v. 
,u,s  iduat.n.   that  son,.  d.-struHiv.   U.ion    ( haMuorrhag.    d. 
structivo  tunu.ur)  exists  on  one  si.!,  of  the  nudbra.n.  so    lu    .t 
iMVolvos  tin.  nnd.us  of  origin  of  tin-  third  n.-rvo  and  a  s<,  the 
nvranndal  fibers  lyi..g  near.    Sin.v  the  fibers  ot  the  th.rd  ne,   .■ 
lu,  not  erass  to  the  opposite  side,  but  those  ot  the  pyranuds  do 
(see  p    2A:\),  we  get  a  crossnl  or  altn;,othu,  parahisis.     Son.e- 
times  onlv  one  part  of  the  third  nerve  nn.y  be  paraly/ed    tor 
..xan.pb-Zthat  portion  going  to  the  nn.seles  of  aeeonuno,lat.on. 
T..K  FciKTii  AM.  Sixth  Nkkvks.-TIu-  fourth  ami  sixth  nerves 
supplv  the  two  extra-m-ular  ninsdes  not  sui.plie.l  by  the  third. 
viL    the    superior   oblique    (fourth)    and    the    external    iretus 

(sixtli).  respt-etiveiy.  .       ,       ,  .      .•   .i.  , 

TlIK    FlhT.l     NKKVK.-The    i\n\    nerve    IS    the    hll-esl     ot       h- 
,,,,nial  nerves,  ami  is  a  rei.n.s,.iitative  inixe.l  nerve.     It  sn,.plies 
the  te.-th      The  .nnlor  hr,tmh   runs  to  tlie  niiiseles  ..t    nuiNtiea- 
tion    the  tensor  nnisele  of  the  pnlale.  the  inyiohyoi.i  n.usele  (m 
the  floor  of  the  nioutiH  and  the  anterior  belly  of  the  .iigastne. 
Thes..  last  two  ineiitioiie.1  inuseles  pull  the  liyoi.l  bone  an.!  then- 
r.„-,.  the  root  ..f  the  tongue  upwanl  and  forwar.l  ^lurnig  the  .n-t 
<,f  vv.allowi.ig.     lioth  niastieation  and  swallowing  are  seru.usly 
i,„,,,in.d  wh  n  this  nerve  is  paraly/ed.     The  s,  „son,  phns  are 
,o,n,eeted  witli  the  reeeptors  for  u\\   tin-  eoininoi.  se'-sat.ons  o 
t,,„  i,„a,l  and  fae,-.     As  already  explained,  they  aiv  e.n.neet  ■- 
Nvitli  the  iierv,.  eells  (d  the  Ca.serian  ganglion,  whieh   is  t  nlge.l 
i„  a   .lepres,sion   near   the  ap.-x  ..f  the   petrous  porlu.n   ol    the 
,,.,„poral  bone.     Shorttv    ifter  leaving  this  ganglion,  the  nerve 
.livi.les  into  thive  bra.:       ,:  (1)  the  upper  or  ophthai.nie.  ean-y- 
i„<'   the  s..nsorv    nerxr    iibers   for   the   ron.junetiva.   the    nu.eons 
,„.Mnb,an,    of  the  nasal  fossa-,  and  the  skin  of  the  eyebrow,  t.nv- 
li.-.d   and   nose       (2>    Mi.hlle  or  superior  maxillary,  sui.plymg 
the  meninges    the  low.-r  eyelid,  the  skin  of  the  side  of  the  nose 
an.l  up|..-r  l,p  nml  all  tlie  t.-eth  ami  gums  of  the  ui.pev  jaw.     ( •!  i 
iMf.ri.n-  inaxiilarv.  supi-lying  the  teeth  and  gums  ot  the  lower 


-^     . 


262 


PHYSIOLOGY  FOR   PFVTAL  STUDENTS. 


tt-  .  ■■  I 


%\ 


jaw,  the  skin  of  the  temple  and  external  ear,  tlie  lower  part  of 
the  faee  and  the  lower  li|i. 

riKI.ATKlNSIHI*  Ob  TIIK  FlKTIl   NkRVK  T(»  TIIK  TkKTII. — III  ah.V  111- 

Haniniatory  eoiidition  (if  tlie  teeth,  the  terminations  of  the  sen- 
sory fibers  iHH'onie  .•stinuilated,  eansing  extreme  pain.  Tliis  is 
toothaehe.  The  relationship  of  the  fifth  nerve  to  the  teeth  ex- 
plains \v'i  disturbanee  in  the  latter  should  often  eanse  the  \m'\\\ 
to  be  referred  not  to  the  tooth  tliat  is  involved,  but  to  some  skin 
area  on  the  faee.  This  is  called  rcfnrcd  pain.  The  skin  areas 
eorresponding  to  th<'  different  teetli  have  lM>en  worketl  out  by 
Uiiid.  nnd  iu  inditated  in  tlie  .iceoinpanyinfr  diagrams  '  Fiijs. 
48  and  49  i.  Not  only  may  the  pain  be  referred  to  the  skin  area, 
hut  tlii^i  ilvli  may  Ixm  mie  hyp(  rsensitivr  Theie  is.  moreover, 
in  each  areii  asually  a  maximal  spot  at  wLii  h  the  pain  .n.d  ten- 
derness are  most  marke«l. 

The  sensory  nerve  <  ndinfrs  in  the  teeth  arc  all  of  the  nature  f)f 
l)ain  receptors;  then  nre  no  temperature  or  tactile  receptors, 
these  latter  s<'n.>,itions  heinjj  particularly  developed  in  the  ton^fue 
and  lips  (see  p.  _'i4  .  The  pain  receptors  of  the  teeth,  like  those 
ol  the  cornea,  react  practically  in  full  intensity  to  every  strength 
of  stimulus.  This  explains  wiiy  a  small  decree  of  irritation,  as 
that  due  to  caries,  mny  cause  as  painful  a  toothache  as  an  in- 
tense irritation.  As  we  have  already  explained,  the  purpose  of 
liiunlul  or  nocuous  sensation  is  protective,  causing,  for  example, 
witiidrawcil  of  the  irritated  portion  of  the  body  or  some  move- 
ment of  offense  (see  p.  2r»l).  In  the  case  of  the  teeth  it  Kcrves  a; 
a  warning  that  something  must  be  done  to  arrest  wli.itcv'r 
condition  is  causing  it.  The  enamel  and  cement  are  devoi<i  of 
nen  e  endings,  which,  however,  are  very  abundant  in  the  i)ulp. 
and  jirobaMy  also  in  the  dental  tubides  (Mummery).  An  inen 
sensationless  exterior  covering,  a  highly  s<'nsitivi;  center,  and 
betwet  n  these  a  moderately  sensitive  tissue,  describes  the  w'lisi 
tiveness  of  a  tooth.  The  sensitiveniss  of  the  pulp  is  so  great  as 
to  suggest  that  it  is  partly  of  the  nature  of  a  highly  specialized 
nrci-reeeptor.  .iust  as  the  taste  buds  ami  olfactory  epitheliiun 
are  specializwl  receptors  for  taste  and  smell.  The  sensitiveness 
of  the  teeth  diminishes  with  advancing  age. 


I''nilili>-n:is:il      iii-iM       ( miixil 
I      liiiy    iiicisiiis). 


M;isill:ii>-  Miia  (  iii:ixilhii.\ 
si'iiiiiil  pii'iniilMi'  iiiKl  lii'st 
iniilar  ) . 

Miiitiil       iinii        (  iimnililiii';!!- 

rst 

|ill  MllllMI). 

Till'   iJiiints   of   in;ixiiiiiiiii    ititriisily    ;ii'>'    lill^;l■ll. 


I INasn-lal.iMl    :.r.-,i     .  m:.xilh.iy     | 1  M.mImI       mi.m        ,  mi.M.lilm^;,. 

1 J      ruiiiH.  i.rnl  tirst  pivMinlMi).     I I       l-»i.s..,s,     ...nin.-     mimI     ImsI 


KiK.  4S. — IHimraiii  tii  slmw  aniis  of  r.fiii.cl  pain  in  ilisti  Mml  ii^ii  >•(  lilili 
IiiTVi'  (lui-  til  afTfrtii.iiH  iif  tlir  variiius  liilh  iKniTil  \  ii  w  I  i  I'l'uMi  iliawiiiu 
liy  T.    Wiiinati'  'riiilii.) 


1.0 


I.I 


1^ 

|7B 

m 

itt 

1^ 

lU 

1^ 

lit 
lu 

b& 

1.4 


1^ 

2.0 


1.8 


1.6 


MICROCOPY  RESOLUTION  TEST  CHART 

NATIONAL  BUREAU  OF  STANDARDS 

STANDARD  REFERENCE  MATERIAL  1010a 

(ANSI  and  ISO  TEST  CHART  No.  2) 


THE   CRANlAr.   NERVES. 


263 


Tlie  fiftli  luTvi'  is  vorv  commonly  th.'  s.'at  of  ncuri.ltrin.  winch 
mav  affect  one  or  all  of  its  brandies.  This  is  .allc.l  •'/„ 
,l,H,loiirr„.r'-  or  tri-facial  ncunilKia.  Th.-  atta.-ks  come  in 
spasHLS,  an.'.  l).-si.l.'s  th.'  ,.xcrucialH>fr  i.ain,  th.-n-  is  often  twitch- 
i„fj  of  the  muscles  or  flushing  of  th.-  skin  of  the-  fac.-.  Pr.>ssi  re 
at  tlic  points  when-  the  branch.-s  of  tlie  nerve  com.-  out  of  the 
skull  as  at  the  supra  or  infra-orbital  n..tch.-s.  is  usually  espe- 
Hallv  painful  in  tic  An  unh.-altliy  .-on.liticm  of  the  teeth  is 
often  responsible  for  the  sympt.mis.  but  if  d.-ntal  tr.-atnu-nt 
and  general  m.-.lical  care  .lo  not  ivmov.-  the  neuralgia,  it  is 
usually  advisabl.-  to  cut  out  a  portion  of  the  n.-rv.-  or  ev.-ii  t.. 
remove  the  entire  (Jasseriuii  ganglion. 

Som.-times  the  fifth  nerv.-  b.-comes  p.mihizrd.  causing  an.-s- 
th.-sia  involving  the  area  ..f  its  .listribution.  Tingling,  numb- 
ness or  lu-uralgic  pains  often  pr.-.-.-d.-  the  anesth.-sia.  Sine.-  tlu- 
eonjunctiva  los.-s  its  seiisitiv.-n.-ss,  i.articl.-s  .)f  .lust.  etc..  are  not 
n-nioved  from  the  .-ye  by  th.-  t.-ars  so  that  th.-y  set  up  inflam- 
mation, which  may  d.-v.-lop  an.l  cause  ulceration  of  the  corn.-a. 
For  the  same  reasmi,  or  perhaps  because  the  n.-rv.-  mdeix-n.l.-ntly 
controls  th.-  nutrition  of  tissu.-s.  the  gums  an.l  .-hecks  may  be- 
come ulcerated  an.l  tlu-  t.-eth  loos.-n,-.l.  Partial  loss  of  tast.-  and 
inability  to  sn..-ll  pungent  vapors,  whi.-h  act  ..n  s.-nsory  n.-rv-s. 
are  also  common  symptoms. 

The  Seventh  NEKVjtLr-Th.-  s.^x.mtli  m-rv.-  is  piir.-ly  motor  m 
function     /-.dTth^-'  facial   muscles,   except   those   conoorn.Ml   in 
mastication,  the  platysma  of  th.-  n.-.-k.  th.-  p,.st.-rior  b.-lly  of  tlie 
di-'astric  and  on.-  of  the  muscles  of  th.-  mi.1.11.-  .-ar    (th.-  sta- 
pedius^  are  supi.li.-.l  by  it.     On  a.-count  of  its  tortumis  .-mirs.- 
the  seventh  nerve  is  p.-eiiliarly  liabh-  to  inflammation  an.l  com- 
lUTSsion.     Thus  tumors  ..r  inflammati.m  locat.-.l  at  th.-  bas.-  of 
the  brain  mav  inv..lv.-  that  i.orti.Mi  running  b.-tw.-.-n  the  upp.-r 
end  of  the  m.-dulla  .oblongata  an.l  th.-  int.-rnal  aii.litory  m.-atus. 
where   tlr     nerve   .-nters   the    a.|U.-.lu.-t    of    Kallopiiis.      In    tins 
r.'gion  it  is  lik.-ly  to  b.-com.-  involv.-d  wli.-n  th.-n-  is  .liseas.-  <)t 
the  internal  .-ar  or  mast.iid  sinus  (mastoiditis).     After  its  exii 
from  tile  skull  (by  tlu-  styhmiastoi.l  f.iramen")  its  .-l.is.^  asso.-iatDii 
with  the  parotid  gland  renders  it  liable  to  be  involved  in  eel- 


264 


Ov- 


PHYSIOLfKJY   FOR   DENTAL   STVDENTS.- 


lulitis  of  this  gland,  and  on  aecount  of  its  superfifial  position, 
it  may  1h'  injured  by  blows  on  thf  side  of  the  licad.  Quite  eoni- 
inoidy  the  seventh  nerve  beeonies  the  seat  of  inflanimatiou  after 
j'xposure  to  a  draught,  as  by  sitting  at  an  oj)en  window.  Tiie 
paralysii  is  almost  always  one-sided.  The  eyeli<l  on  the  affeeted 
side  cannot  be  properly  closed,  a  chink  remains  and  the  eyeball 
becomes  rotated  upward,  thus  showing  the  sclerotic.  On  smiling 
or  showing  the  teeth  the  mouth  is  drawn  up  on  the  healthy  side, 
causing  a  triangidar  opening  because  the  lips  do  not  become 
separated  on  the  i)aralyzed  side.  Articulation  is  difficult  and 
such  acts  as  whistling  and  blowing  are  impossible.  Hecausc  of 
I)aralysis  of  the  buccinator  muscle,  food  colh-cts  betwicn  the 
cheek  and  gums.  The  distortion  of  the  face  is  much  more  y)ro- 
nounced  in  old.  tium  in  young  persons;  indei'd  in  the  case  of 
the  latter  the  paralysis  may  be  overlooked  until  speaking  or 
laughing  is  attempted. 

The  KuiiiTii  ok  Aiditoky  Nekve. — The  eighth  or  auditory 
nei've  is  composed  of  two  branches,  tin-  one  called  vochhtir,  con- 
nected with  the  organ  of  Corti  (see  p.  2!H),  which  collects  sound 
waves,  and  the  other,  called  nsfibiihir,  with  the  semicircular 
canals  which,  by  the  movements  of  the  fluid  contained  in  them, 
record  changes  in  the  position  of  the  head  (see  j).  276).  Hoth 
branches,  being  sensory,  are  connected  with  ganglia  situated  in 
or  near  the  internal  ear  (ganglion  s|)irale  for  the  ( nchlear  di- 
vision and  ganglion  of  Scarpa  for  tiie  vestibular).  I'arnlysis 
of  the  auditory  nerve  cau.ses  a  degree  of  deafness  which  is  nioic 
proftmnd  than  that  due  to  disease  of  the  middle  ear.  for  in  the 
latter  case  a  tuning  fork  can  be  heard  when  the  end  of  it  is 
applied  to  the  skull  or  is  held  in  the  teeth,  which  is  not  the  ea.se 
when  the  nerve  is  diseased.  When  the  eighth  nerve  becomes 
irritated  (as  by  inflammation  of  the  ear.  or  a  general  comlition 
such  as  migraine,  epilepsy,  etc.),  various  kinds  of  sounds  are 
heard.  Tiiis  is  called  finnitHs.  It  is  not  infreipjently  followed 
by  deafness. 

The  Ninth  ok  GEosso-pnAKYNdEAE  Nerve. — The  ninth  or 
glos.so-pharyiigeal  nerve  is  partly  motor  and  partly  sensory. 
The  motor  libers  sui)ply  the  muscles  of  the  pharyn.v  and  most  of 


Tfniporal      aiou       ( maxillaiy 
second   pivmolart. 


Hyoid  MifM  (mandibular  sec- 
ond prt'niolar :  tiist  .iiid 
Sfi-ond    molars). 


Mandibul 
second 

lars). 


ar    ;  rea    (maxillary     I""        |   Superior     laryngeal    area 
and     third     premo-     '——J        ( mamliltular  third  molar  t. 


The  points  of  maxinr;  a  intensity  are  rinKed. 

irjjj.  4!!. — Dianram  to  show  areas  of  referred  pain  in  dislrilmtion  of  fifth 
nerve  due  to  affeclions  of  tile  v 'lious  teetli  (Side  view).  (Fro  IrawinK 
by  T.   WIngate  Todd.) 


& 

t 

i 

f 

I 

1 

^ 

! 

TDK   CKANlAIi    NKKVKS. 


2G."i 


tl,„s,.  of  tl..'  soft  i»alatr.  Tlu"  s.M.Hory  fib.TS  .-arry  inM.uls..s  of 
common  sn.satio..  an.l  of  tast.-  from  .1...  root  of  tl...  ton«u..  th<- 
,uMKl.lK.nns  portions  of  tl..'  pliarnyx,  tlu-  tons.ls.  tin-  sott  palat-. 
„n.l  tho  pillars  of  tlu-  fauc-.s.  This  n.-rv.  .lo.s  not  connnonly 
bf.'omt'  thf  st'at  of  local  lesions. 

Till-  Ti-NTii  OH  V.uns  NKKVK.-Tl.is  is  tlu-  mam  ccrchrospnial 
ncrvr  supplvin-  the  viscera  an.l  it   is  lu.th   motor  an.l  s..ns..ry 
in  function."    Wc  shall  s.-e  lat.-r    that  tlu-  n..rves  t..  th.-  v.s.vra 
hclon.'  to  th.'  so-call.Ml  autonomic  system,  whifh  is  .i.stn.«uish...l 
from  "the  somatic  by  two  main  facts,  one  anatonncal   a>i.l  on.' 
functional.    The  anatomical  diff.-ren.-.-  is  that  .-v.-ry  nerv.-  hb.-r 
bccom.'s  conn.'cte.!   through   synaps.-s  with    n.rve   c.-Us   locat.'.l 
peripherallv  (i.  e..  n.-ar  the  end  of  the  nerve),  an.l  tl..-  ax.ms  oi 
th..  ..-lis  .-ontinue  th.-  impuls,-  on  to  the  structure;  th.'  lunct.onal 
ditfercnc..  is  that  tlu-  auton.m.ic  fib.M-s,  as  th.-ir  nam.'  ui.licat.'s 
cntrol  antomati.-ally-actinn  ..r  inv..luntary  functn.ns  inst.'a.l  ot 
voluntary  movm.'nts.  as  is  th.-  cas.-  with  th.-  ..r.hnary  ..r  somat... 
cei-ebrospinal  n.'rv.'  fibers. 

Th.'  most  important  of  th.'  vajrus  aul.>nomic  fib.'rs  run  to  th.' 
heart  (s.-e  p.  is:.).  the  o-sophaKUS  (p.  'nK  the  stomach   U'-  •'"' 
an.l  the  int.-stin.'s   (p.  7!»).     Th.'  vai.M.s  also    ....ntams    atl.'r.'ut 
fibers  which   hav.'  th.-ir  .-.'11  stations  in  gan^'lia  situat.'.l  m  tin 
trunk  of  the  n.'rve.     Th.-s,-  fib.-rs  carry  s.'usory   nMpuls.-s  par 
ticutarlv  fron.  th.'  laryn.x  an.l  lun-s  ( ,..  21!)'.     Kurth.'r  .l.'ta.ls 
n.>;ar.lin<r  the  fun.-tim.s  controlh'.l  by  th.-  va-us  are  tuUy  -ivn 
i„  Th.'  r.'fer.'n.-es  in.licate.l  abov.'.     Wh.'U  th,'  va-us  n.rve.  .n- 
its  cnt.'r.  is  th..  seat   .)f  paralysis,  swall.)winK  is  s.-riousiy   ,n- 
t,.i'n'r.'.l   with,  an.l  food  is  liabl.'  to  pass  int..  tii.'  larynx   an-l 
cans.'  pneumonia.     Vari.ms  f..rms  of  paralysis  of  the  v.H-al  .'..r.ls 
mav  also  result  from  j.aralysis  i»f  th.'  vajrus. 

TlIK    Kl.KVKNTll    ..If    Sl-iNAI,    .\(CKSS.  .KV    .N  KKVK.— Th.'    .'!.  V.'Ulh 

01'  sj.inal  a.-...'Ssory  is  entir.'ly  an  etr.'r.'nl  n.-rve.  ..n.'  part  ..t 
it  the  acc.'.ssorv,  l.eins:  .l.'riv...!  from  the  same  .-olumn  ..t  n.Tv.' 
c'us  as  th..  vajrus  an.l  b.'intr  r.'ally  a  part  of  this  n.rv.-;  tl... 
other  arises  from  the  c.-Us  ..f  th..  ant.'ri.-r  h..rn  of  th.'  spinal 
cor.1  in  the  upp.'r  .-ervical  re-ion  an.l  supplies  the  trap.'/ius  an.l 
stcrno-mastoid  muselcs. 


206 


I'llYSIOliOOY   FOR   DENTAL   STUDENTS*. 


TlIK    TWKLKTII    OR    IlYI'OfJI-OSSAI,    NkKVF,.— TIlC    tWflftll     lltTVC 

or  liypogloHHjiI  is  ciitirt'ly  cffi'i-i'iit,  IwiiiK  the  iiiot(»r  iktvi-  of  tin- 
tonpuo  muscles  and  of  iiiost  of  tlif  iniisclfs  attachtvl  to  the  hyoid 
bono.  Wlicn  it  is  paralyzed,  as  in  bulbar  paralysis,  swallowiujr 
of  food  becomes  impossible,  the  toiitfue  cannot  be  protruded 
and  soon  atrophies  because  of  the  removal  of  the  trophic  in- 
fluence of  the  nerve  cells.  Rarely  the  jtaralysis  is  unilateral, 
,»ut  this  is  because  of  lesions  higher  up  in  the  nervous  system 
than  the  medulla  and  so  situated  that  they  destroy  the  con- 
nection of  the  fibers  which  run  from  the  higher  motor  centers 
in  the  cerebrum  to  the  hyi)oglo.ssid  micleus.  Such  lesions  neces- 
sarily involve  fibers  of  the  same  type  running  to  the  nerve  cells 
of  the  spinal  cord,  so  that  hemiplegia  (p.  24H)  accompanies  and 
is  on  the  same  side  as  the  tongue  i)aralysis.  When  a  patient 
with  such  a  lesion  attempts  to  put  out  the  tongiie,  it  is  directed 
towanls  the  atfcctinl  side  but  it  shows  no  atroi)hy. 


CIlArTKK  XXVIII. 

TlIK  NKUVOrS  SYSTKM    ((V)iit\n. 

The  Brain. 

Tlic  first  iiiiostioii  which  naturally  arises  is,  wliat  iiitluciif*' 
(Iocs  the  brain  have  on  the  rctlcx  movements  produeed  tlintuiih 
the  spinal  eord?  Tliew  influences  may  he  summarized  as  fol- 
lows : 

1.  The  brain  enables  the  aninnil  to  will  that  a  particular 
niovinieiit  shall  or  shall  not  take  place,  irrespective  of  the  stimu- 
lation of  spinal  reflexes.  Much  of  this  influence  of  the  brain  is 
of  oours<'  voluntai-y  in  nature,  but  some  of  it  is  subconscious  or 
involuntary.  In  general  it  may  be  saitl  that  the  cerebrum, 
through  the  jiyramidal  tracts,  usually  .-xereises  a  damping  «)r 
inhibitory  influence  on  the  spinal  reflexes.  Tt  is  for  this  reason 
that  the  reflex  response  to  a  certain  stimulus  is  usually  nnich 
more  pronounced  in  a  sj)inal.  as  compared  witii  a  normal  animal. 
For  example,  it  is  impossible  to  bring  about  the  scratch  reflex 
in  many  normal  dogs,  whereas  it  is  always  present  in  spiiud 

animals. 

In  man  this  restraining  influence  of  the  pyramidal  tracts  on 
si)inal  reflexes  is  very  evident  in  the  case  of  the  knee  .jerk,  whi<'h. 
it  will  be  remendjered,  is  the  extension  of  the  leg  which  occ\irs 
wh.'U  the  stretched  patellar  ti'udon  is  tapped.  Ordinarily  the 
kick  is  nmderate  in  degree,  but  in  i)atients  whose  pyramidal 
tracts  are  diseased,  as  in  spastic  paraplegia,  it  becomes  very 
l)ron(mnced. 

2.  The  biain,  being  the  receiving  station  fen-  the  pro.jicient 
sensations  (p.  27!M,  sight,  hearing  and  smt  ..  adds  greatly  to 
the  number  of  aft'erent  pathways  by  which  reflex  actions  can 
Ik  excited. 

3.  Since  in  higher  aninmls  all  the  atl'eren*  impulses  usually 

267 


268 


l'llvsinl,(HiV   FUR  DENTAI-  STri»ENTS. 


fl! 


travel  throuKh  the  bniiii  (i».  24H).  iiiiiny  iutvi-  ciMitt'i-H  bi-comc 
more  or  less  iiivolviMl  in  tlif  r-Hix  actioiiH.  so  that  a  imi«-li  IiIkIh  r 
(It'frn'c  <»f  co-onliiKitioii  than  tli  i  seen  in  a  spinal  animal  attcndH 
the  iniiM'ular  rt'sponsc.  Fnr  txaniplc,  sonu'  nt'  these  afTerent 
impulses  reach  the  cerehellnni.  whose  function,  as  we  shall  see. 
is  to  strengthen  some  impn!.s«'s  and  weaken  others,  so  that,  a 
more  |)erfect  movement  results. 

4.  The  animal  hecomes  conscious  not  only  of  tiie  imture  and 
plaei-  of  api)lication  of  the  sensory  stimulus  itself,  hut  of  the 
dejjree  to  which  it  has  moved  its  muscles  in  respotise. 

The  Functions  of  the  Cerebrum. 

The  compli<'ated  movements.  su<-h  as  those  involved  in  the 
scratch  refle.x.  which  we  have  seen  that  a  s|)inal  animal  can  carry 
out  in  the  i)aralyze<l  rej;ion  after  shock  has  pa.s-sed  away,  become 
more  and  more  numei-ons  and  comi)licated  as  the  hi^lier  centers 
are  left  in  connection  with  the  spinal  conl.  That  is  to  say.  the 
hijfher  up  in  the  cerebrospinal  a.xis  that  the  section  is  ma<le,  the 
more  ca|)able  does  the  [lart  of  the  animal  below  the  section  be- 
come to  peform  complicated  movements.  The  important  centers 
in  the  mei'  da.  pons  and  mesencephalon  add  their  intlueiice  to 
those  of  ,..'  sjtinal  cord  itself,  so  that  intcjiration  becomes  more 
comprehensive.  If  the  cut  is  made  above  the  level  of  the  i)ons, 
in  other  words,  if  the  cerebral  hemispheres  alone  be  discon- 
nectetl  from  the  rest  of  the  cerebrospinal  axis — fhtrnhrdtion, 
as  it  is  called — we  obtain  an  animal  possessinj;  all  the  retlex 
actions  that  are  necessary  for  its  bare  existence,  althoufjli  it  is 
of  course  inca|)able  of  feelinj,'  or,  if  the  basal  nanfflion  be  also 
destroyed,  of  s-'cing  or  hearin-.'.  It  becomes  a  mere  automaton: 
it  breathes,  the  blood  circulation  is  normal,  it  can  walk  or  run 
or  swim,  it  swallows  food  if  the  reflex  act  of  swallowing  be 
stimulated  by  placing  the  food  in  the  mouth,  but  it  has  not  the 
.sense  to  take  f(M)d  itself  .-ven  when  this  is  placed  near  it.  All 
the  mental  processes  are  absent:  it  has  no  memory,  no  volition, 
no  likes  and  di.slikes.  liy  seeing  that  it  takes  fo(Ml.  it  1  i-'  been 
iwssible  to  keep  such  a  decerebrated  dog  aliv<"  for  eigiitwn 
months,  and  the  lower  we  descend  in  the  animal  scale,  the  easier 


TIIF  KINCTIONS  OK  TIIK,  (  r.HKI«HrM. 


•_'f.!» 


it  Iweanu'M  to  iicrfonn  tin-  oiM-ratioii  iiiul  to  ki-i'p  tin-  aiiiinal  alive. 
Ill  iiiKht'i-  Hniinals,  siicli  as  inoiik.-vs.  howfViT.  lift'  is  iin|>i>s.sihl.' 
without  tin-  (•.•rt'hniiii.  thus  supportiiit,'  the  conclusidn.  which  w- 
have  alr.aily  .Irawii   (stv  p.  24:{).  that  th.'  (■.ivl.niiii  coiu.-s  to 

1„.  ;i  III ssary  part  of  every  retlex  action  in  th.'  Iiijjher  animals. 

Cerebral  Localiiation.— The  varinus  runelimis  of  the  cere 
liruin  are  located  in  ditfereiit   portions  of  it.     This  liM-aii/ation 
(if  cerebral  functions  lias  lieeii  very  extensively  studied  duriiitf 
recent  years,  partly  by  exiieriinental  work  on  the  higher  niam 
nialia  and  iiartly  by  clinical  studies  on  man.     Careful  observa- 
tions are  made  of  the  behavior  of  the  various  functions  of  the 
animal  either  after  removal  or  destruction  of  a  portion  of  the 
cer.'iiiinn.  or  during  its  stimulation  by  the  electric  current.     Im 
portant  ailditions  to  o\ir  knowledUe  of  cerebral  localization  are 
also  beinn  maile  by  eorrclatinjf  the  symi>toms  observed  in  insane 
persons   with    the    lesions   which    are    revealed    by    post-ninrteiii 
examination. 

It  has  been  found  that  there  are  roughly  t!ree  areas  on  the 
cerebrum   with  distinct  and  separate  functions   (  Kiy.  .'lO). 

I.  In  the  jiortions  of  the  cerebrum  which  lie  in  front  of  the 
ascending,'  frontal  convolutions — [tn  frontal  nuioii— art'  located 
the  cente  of  the  intellect  (thouKht.  ideation,  memory,  etc.). 
Tills  part  of  the  cerebrum  is  aecordin«ly  by  far  the  best  de- 
velofied  in  man ;  it  is  much  less  so  in  the  apes  and  monkeys 
becomes  insignificant  in  the  dog,  and  still  more  so  in  the  rabbit. 
It  has  been  destroyed  by  accident  in  man  with  the  result  that 
all  the  higrher  mental  |)ower.H  vanished. 

II.  The  i!','xt  i>ortion  includes  routrhiy  the  re<rion  of  the 
cerebrum  bordering  upon  the  HoUtiidic  fix.siirf  (i.  e..  the  ascend- 
ing frontal  and  ascending  iiarietal  convolutions).  Here  are 
located  the  highest  centers  for  the  movements  of  the  various 
jiarts  of  the  body.  Microscopic  examination  of  the  grey  matter 
reveals  the  jircsenec  of  large  triangular  nerve  cells,  which  com- 
municate by  synapses  (see  j).  241)  with  the  atfereiit  fibers  tiiat 
carry  the  sensory  imi)ulses.  whose  course  from  the  jmsterior 
spinal  roots  we  have  already  traced  (p.  246 j.  From  each  of 
these  cells  an  etferont  fiber  runs  to  join  the  jiyramidal   tract 


270 


PHY.^IOUKiY    VOR   OKNTAf.   STIT>F.\TS. 


HI  i 


(p.  248).  nml  tlius*  (Mimu-H  with  lli.'  iiiitfrior  lioni  cflls  of  the 

spinal  pord. 

l!i  the  liuhindU  ana,  as  it  is  CHllcd,  is  tli.n'forc  sitiiatftl  Ww 
iH'ivbral  link  in  tin-  rliaiii  of  iiciiroins  (s«m'  i».  24!t)  through 
wliieh  tlif  oniiiiary  luovcnu-nts  of  tlu'  IxMly  taite  place.  Such 
iiiovt'iiU'iitH  iiia.v  Ih-  set  ajfoiiift.  <'itlifr  by  stimulation  of  tlic 
Holandii'  n.  rvc  cflls  through  atTcn-nt  filM-rs— a  pmv  ivH.'X— or 
by  impulses  coniinK  to  tlx-ni  from  tlu-  i-nt«"rs  of  volition  situated 


KiK.  r.0.— ("Drtloal  centfiB  in  iiiiin.  Of  the  thitv  Hhiul.d  airas  boiil.-iiiiK  on 
the  Holamlie  tlMMure  (ffof.).  the  most  anteiior  is  the  preceiUral  iissmriatUinal 
area,  the  middle  one  is  the  motor  area  (the  poHitioii  of  the  l.ody  areas  ar. 
iiKlle'ateil  on  it),  and  the  most  posterior  is  the  sensory  area,  to  the  lells  oi 
which  the  fillet  Hb.rs  proceed.  The  centers  for  seeinR  and  hearing  an-  also 
shown.  The  unshaded  portion  in  front  of  the  l{olan<lic  area  is  the  precentral 
the  portions  liehind,   the  parietal  and   teinperospheiinidal. 

in  the  prefrontal  eonvolutions.  Or,  again,  the  nerve  cell,  at  the 
same  time  that  it  receives  a  sensory  impulse  coming  up  fr(»m 
tile  spinal  cord,  may  receive  one  from  the  prefrontal  eonvolu- 
tions which  may  either  int^'rdict  or  greatly  modify  the  ivtle.x 
response.  Kvery  possible  muscular  j^roup  in  the  body  has  a 
center  of  its  own  in  the  Rolandic  area,  the  determination  of  the 
exa-  )cation  of  these  centei-s  being  one  of  the  achievements 
of  i.Lodern  medical  science.    Thus,  if  we  stimulate  with  a  finely 


TIIK  KINCTIONS  tiK  TIIK  CIIIKIlKr  M. 


>trn(I<'<l  fit'ct  I  stii  jlu«.  my,  tlif  ct'iitcr  of  tlir  thiiiiili.  it  will 
1)1'  found  that  t>'  .liuiiib  uiidiTiiois  a  slow,  purposcriil.  i'o-i,.ili 
iiat'ii  iiiovciiiciit :  and  so  on  fur  tvtry  otln  '  i-t-ntcr.  Or,  if  in 
Ntrad  of  MtiniiilatinLT.  w«'  cut  away  one  <if  .>•  rt-ntt'is  and  allow 
the  animal  to  rta-oV'  r  from  the  iminrdiatc  ctTrcts  of  the  opera- 
tion, it  will  hv  found  that  all  the  more  finely  eo-ordinated  move- 
ments of  the  eorresj)  )Mding  part  of  the  IiikIv  hase  disappeared. 

alt  hough  K'"'*'*  reHex  niovenieiits  may  he  possible,  1 ause  tlie 

^piiud  retlexes  are  still  intact.  Jf  the  entire  Kolandic  area  on 
nuv  si<l('  is  removed,  the  mustdes  of  the  opposite  sich'  of  the  h(»dy 
except  thoHc  of  the  trunk,  become  com  •ely  paraly/ed  for 
some  time,  after  which,  however,  )>artic,  -ly  in  tlie  .-ase  of 
younu  aninuds,  the  paralysis  becoi  is  iict.vcred  from,  thus  in- 
dieatinur  that  Home  other  i)ortu)i;,  )f  the  brain  have  assumed 
the  function  of  the  destr  ved  cent  >  If  the  stimulus  is  a  very 
stntnj?  one,  the  movenii  ^  do  not  i  nuiin  confined  to  the  cor- 
res,,.  idiny  musdi  f^roup,  but  the.v  spread  on  to  neijfhboriiif; 
jrroups  until  ultimately  the  whole  extremity  or  |>erhaps  i  ten 
all  the  muscles  of  that  .side  of  the  body  arc  involved. 

These  experimental  results  find  their  exact  counterj'Mrt  in 
)li)ii<(il  ( j-pi  rifiKi .  Thus  when  some  center  becomes  irritated 
by  i)re.ssure  on  it  of  some  tumor  >»rowinj?  in  the  membranes  of 
the  brain  (meningeal  tumor),  or  by  a  piece  of  bone,  as  in  de- 
pressed fracture  of  the  skull,  or  by  blood  clot,  convulsive  at- 
tacks (known  as  Jacksonian  epilepsy)  become  common.  The 
fir.st  sign  of  such  an  attack  is  v  lally  some  i»eculiar  sensation 
(aura)  affecting  th.e  part  of  the  body  which  corresponds  to  the 
irritateil  area,  then  the  nuiscles  of  this  part  begin  to  twitch  and 
more  muscles  get  involved  until  ultimately  all  those  of  the  coi-- 
responding  half  of  the  bod.v  become  contracted.  There  is.  how- 
ever, no  loss  of  consciousness,  which  there  is  in  true  epilej)sy. 
The  evident  cause  of  those  symptoms  has  clearly  indicated  the 
proper  treatment  for  such  cases,  namely,  surgical  removal  of 
the  cau.se  of  irritation.  Fi.r  this  purpose  a  very  careful  .study 
is  first  of  all  made  of  the  exact  i-ouj)  of  muscles  in  which  the 
convulsions  originate,  the  location  of  the  area  on  the  cerebrum 
is  thus  ascertained  and  a  trephine  hole  is  made  in  the  correspond- 


272 


I'llYSI(»I,(><iY    F(1R    DF.NTAI.    STn>i;\TS. 


iiij,'  j>ai't  of  the  craiiium  and  tlirough  this  liolc  the  tumor  or 
])lootl  c'l  t   is  rciiiovt'd. 

111.  Tlicsf  so-called  motor  areas  are  of  course  also  snisorif 
areas  in  the  sense  that  the  atrerent  stimuli  which  come  up  from 
the  spinal  cord  run  to  thi'in.  They  are  really  sens<>ri-nu)tor 
centers.  For  some  of  the  more  hifjhly  specialized  proficient 
sensaticnis  such  as  vision  and  hearino;  (see  p.  2T'.M,  tlir  -  are, 
however,  special  centers.  These  alonpr  with  an  extensive  field 
of  as.socialiona1  or  junctional  yrrey  matter  constitute  the  third 
nuiin  division  of  the  cerehral  cortex  and  occupy  the  t?reater 
liart  of  the  i)arietal,  the  temporosphenoidal  .and  the  occipital 
lobes.  The  risi(((l  is  the  most  definite  of  these  centers.  Thus 
if  the  occipital  lobe  he  removed  or  destroyed  by  disease  on  one 
si(h'.  tile  correspondinj,'  half  of  each  retina  becomes  blind.  It 
is  by  studyintr  the  exact  nature  of  the  involvement  of  vision  in 
sucli  cases  that  the  physician  is  able  to  locate  the  position  of  a 
tumor,  etc. 

The  center  for  lunrinn  is  in  the  temi)orosphenoidal  lobe,  hut 

its  location  is  not  very  definite. 

It  will  be  seen,  however,  that  the  visual  and  auditory  centers 
take  ui>  but  a  small  part  of  this  third  division  of  the  cerebnun, 
the  most  of  it  Ix'in},'  occupied  by  (iss<j<  iotioital  firias.  The  nerve 
cells  of  these  areas  do  not.  like  tiiose  of  tlu'  motor  and  sensory 
centers,  send  fibers  which  run  as  pyramidal  or  optic  fibers  to 
some  lower  nerve  center,  but  only  to  other  cerehral  centers, 
which  they  sei've  to  link  tojrether.  They  are  specialized  to  serve 
as  Jun.-tion  ])oints  for  all  the  receivinij  and  discharg:in<r  centers 
of  the  cerebrum,  so  that  all  actions  may  be  properly  correlated  or 
integrated.  These  .junctional  centers  thus  i)erform  the  fjreat 
function  of  ada|)tin}.'  every  action  of  the  entire  aninuil  to  some 
definite  purpose.  Aloufr  with  the  nerve  cells  in  the  prefrontal 
areas,  the  assoriational  cells  represent  the  hijfhe.st  developnu-nt 
of  eei'ebral  inte-rration.  so  that  we  find  the  areas  in  which  they 
lie  to  become  more  and  nu)re  pronounced,  the  higher  we  ascend 
the  animal  scale. 

The  Mental  Process.-  The  impression  received  by  the  visual 
center  when  a  young  animal  looks  for  the  first  time  at,  say  a 


TJIE  FINCTIONS  OP  THE  CEREBRIM.  ^lo 

Im'U,  becomes  stored  away  in  nerve  eells  lyins  in  or  close  to  that 
center,  and  wlien  the  bell  is  moved  sound  memories  are  lii<e\vise 
stored  in  the  auditory  center.  At  tirst  tlu'se  remain  as  isolated 
memory  impi'essions  and  the  animal  is  unable  to  a.ssociate  the 
sijjht  with  the  sound  of  the  bell  Hut  later,  with  repetition,  the 
visual  and  the  auditory  centers  become  linked  top'ther.  throujrh 
nerve  cells  and  fibers  which  occupy  the  a.s.sociatioiud  areas,  so 
that  the  invocation  of  one  memory  is  followed  by  assiwiation 
with  others.  It  is  evident  that  the  intricacy  of  this  interlace- 
ment of  diffv  lit  centers  will,  in  larjre  part,  determine  the  in- 
tellectual development  of  the  animal,  and  the  possibility  of  his 
learning  to  judge  of  all  the  con.se(|uenees  that  must  follow  every 
impression  which  he  receives  or  every  act  vshich  he  ])erforms. 
In  man  these  as.sociational  areas  are  very  pooi'ly  developed  at  the 
time  of  birth,  so  that  the  human  infant  can  perform  but  a  few 
acts  for  itself.  Everything  has  to  be  learned,  and  the  learning 
process  goes  hand  in  hand  with  dev«loi)nient  of  the  associational 
areas,  which  proceeds  through  many  years.  On  the  other  hand, 
most  of  the  lower  animals  are  born  with  the  associational  areas 
already  biid  down  and  capable  of  very  little  further  increase, 
so  that,  although  nuich  more  able,  than  the  human  infant,  of 
fending  for  itself  at  birth,  the  lower  animal  dm-s  not  afterwards, 
develop  mentally  to  the  same  extent. 

The  practical  application  of  the.se  facts  concerning  the  func- 
tions of  different  areas  of  the  cerebrum  is  in  the  study  of  mental 
disea.ses.  To  serve  as  an  example  we  may  take  (iphnsiu.  This 
means  inability  to  interpret  sights  or  sounds  or  to  express  the 
tlunights  in  language.  In  the  former  variety — called  sensory 
aphasia — the  i)atient  can  .see  or  hear  ))erfeetly  well,  but  fails 
to  recognize  that  he  has  seen  or  heard  the  object  before,  lb- 
fails  to  recognize  a  printed  wttrd  (word  blindness)  or  to  in- 
terpiet  it  when  spoken  (word  deafness).  The  lesion  responsible 
for  this  condition  is  located  in  the  associational  areas  and  not 
in  the  centers  tliem.selves.  In  tlii'  other  variety,  called  motor 
aphasia,  the  patient  understands  the  meaning  of  soun<ls  or 
sights,  of  spoken  or  written  words,  but  is  unable  to  express  liis 
thoughts  or  impressions  in  language.    The  lesion  in  this  case  in- 


274 


lMIYSI(lI.(MiY    FdU    DKNTAI,   STII>K.NTS. 


|i  '! 


volv.'s  son...  of  tlw  (M.iit.TS  i.onc.'r.i.Ml  in  the  lii^'hor  control  of 
th."  nnis.-l(s  wliicli  an-  iis.'.l  in  si.r..cl..  and  very  .•onin.only  it  is 
situat.Ml  in  tiic  l.-ft  si.!.-  of  ti..-  (•.-n-hrnni.  In  all  thr.-e  forms  of 
aphasia  tli.T.'  is  more  or  l.-ss  dc-n-asc  in  th.-  ni.Mital  powers. 

Cerebellum. 

Ti.c  atr.Mvnt  inii)iilscs  s.'t  up  by  stinnilaiion  of  the  nerves  of 
tile  hkin  in  a  spinal  animal,  and   due  therefore  to  ehauKes  in 
the  (iivironment.  after  .■ntering  the  spinal  eord  travel  to  the 
various  eeiit.-rs  in  the  eor.l.     Althoufih  eomi)lieated  movements 
niav  result   (e.ft..  the  srrateh  reflex),  there  is  an  entire  absence 
of  the  power  of  maintaining  bodily  e.|uilibrium,  and  the  animal 
cannot  stand  because  the  muscles  are  not  kept  in  the  degree  of 
ton.-    which    is  necessary  to  k.-ep  the  joints  properly  stiffened 
A   similar  inability   to  maintain   tlw  center  of  gravity  of  the 
body  results  from   removal  of  the  cerebellum,  or  .small   brain, 
which   it  will  be  r."memb»-red  is  situat.-d  dorsal  to  the  medulla 
iind  pons,  with  whicii  it  is  connected  by  thnv  peduncles.     The 
crebelliim   consists  of   two  hit<  ml  Jomisphfrrs  and  a   median 
lobe  called  th,    nrmis.     The  remarkable  infol.ling  of  the  grey 
matter  which   composes   its  surface,   and   the  large   number  of 
nuclei  which  lie  eiidu'd.led  in  its  central  white  matter  are  struc- 
tural peculiarities  of  the  cerebellum. 

Th.-  imm.-.liate  results  of  removal  of  the  cen-b.-llum  consist  in 
.-xtr.-me  restl.-s.sn.-ss  and  inco-or.lination  of  movements.  The 
animal  is  con.stantly  throwing  its.-lf  about  in  so  violent  a  man- 
ner that  unless  controlled  it  may  dash  itself  to  death,  (h-adually 
the  .■.Kcitement  gets  l.-ss  until  aftt-r  several  weeks  all  that  is 
noticed  is  that  there  is  a  condition  of  muscular  wi-aknc-ss  and 
tremor,  and  difli.-ulty  in  maintaining  the  body  e.|uilibrium. 
Quite  similar  symptoms  occur  wh.-n  the  cen-belliim  is  .liseased 
in  man  (as  by  the  growth  of  a  tumor),  the  ..'oiLlition  being 
call.-d  c.-r.-b<-liar  ataxia,  and  being  characteriz.'d  by  the  uncer- 
tain gait  which  is  like  that  of  a  drunken  man. 

These  ob.st-rvations  in.licate  that  the  function  of  the  c.-rebellum 
is  to  harmonize  the  actions  of  the  various  muscular  group.s.  so 


Tin;    FINCTUINS  OF   Till.   CKliKRI'.I.I.l'M. 


:(.) 


tliat  any  (iisturlmiict'  in  tin-  I'l'iilcr  of  jjnivity  ol'  Ihc  ImhIv  in.iy  he 
subconsciously  rcctifi<'(l  Ity  iipproid-iatc  action  of  the  various 
muscular  groups.  It  evidently  represents  the  nerve  center  liav- 
iiiff  supreme  control  over  other  nerve  centers,  so  that  these  may 
not  brinj;  about  such  movements  as  would  disturb  the  i<iniii- 
briinti  of  tin  nuimiil. 

Ill  order  that  the  cerebellum  may  i)erform  this  function  it 
must,  liowever.  be  informed  of  two  thiii'rs.  In  the  first  i)lace,  it 
must  know  the  existing,'  state  of  contraction  of  the  muscles  and 
the  tinhtness  of  the  various  tendons  that  pull  upon  the  .joints, 
and  in  the  second,  it  must  know  the  exact  position  of  the  center 
of  !?ravity  of  the  body. 

Information  of  the  condition  of  the  muscles  and  teiubtns  is 
supplied  through  the  ikwis  of  nmsclr  sitisi,  which  run  in 
every  muscular  nerve  and  are  connected  in  the  muscles  with 
l)eculiar  wnsory  nerve  terminations  called  muscle  spindl'.'s. 
When  the  muscles  contract,  or  the  tendons  are  put  on  the  stretch, 
these  spindles  are  compressed  and  senso"y  or  at^'ereiit  stimuli 
j)ass  up  the  nerves  of  muscle  sense,  enter  the  cord  by  the  i)os- 
terior  roots  and  reach  the  cerebellum  by  way  of  the  lateral  col- 
umns (see  p.  24!!) . 

Information  refrarding  the  centi-r  of  firavity  of  the  body  is 
supplied  througli  the  vestibular  division  of  the  eijilith  nerve, 
which,  it  will  be  recalled,  is  connected  with  the  s(  })n(  imilur  laii- 
<ils  and  vestibule.  In  these  sti'uctures  are  meiidtranous  tubes  or 
sacs  oontainiiifi  a  sensory  orfjan  (called  the  crista  oi"  macula 
acoustical,  wliicli  consists  essentiall.v  of  [groups  of  columnar  cells 
furnished  with  very  tine  hair-like  processes  at  their  free  ends 
and  connecti'd  at  the  other  end  with  the  fibers  of  the  eifrhth 
nerve.  The  hair-like  i)r(ioes.ses  float  in  the  fluid  which  is  con- 
tained in  the  meiidn-anoiis  canals  or  sacs.  This  fluid  does  nat, 
however.  coiiM)letely  All  these  structures,  so  that  it  moves  when- 
ever the  head  's  .aoved.  This  movi'inent  atVects  the  hair-like 
processes  and  thus  sets  up  nerve  imi)ulses  which  are  carried 
to  the  cerebellum. 

To  make  the  hair  cells  of  this  receiviufj  appai'atus  capable 
of  responding  to  every   possible   movement  e     thi'   head,   it   is. 


276 


PIIYSIOLCKiY    FOR    DKNTAL    STinENTS. 


m 


m 


however,  .-vi.l.'nt  that  there  must  be  some  doflnite  arrangement 
of  the  tubes.  This  is  provLle,!  fof  in  the  disposition  of  the  semi- 
<.ireular  eanals  in  three  ph.nes.  namely,  a  horizontal  and  two 
vertical  ( Fig.  r,l ) .  Taken  together  the  thre."  eanals  form  a  struc- 
ture which  looks  somewhat  like  a  chair,  the  horizontal  eanals 
bei]ig  th.-  seat  of  tlie  chair  and  the  two  vertical  canals  joining 
together  to  form  its  back  and  arms.  The  back  of  each  chair  is 
directed  inwards  so  that  they  are  back  to  back.  At  one  end  of 
each  canal  is  a  swelling,  the  ampulla,  in  which  the  sensory  nerve 


Ki.    -,1  -Tho  s..mUir<ular  ...nals   of   th.   ...r,   slu.winK   Uwir   :.rn.n«,.m..nt 
Jut  thr.-  Han..s  of  s,...-...      (Kron,   Howlls   |-l,y«iolo«>.) 

apparatus  above  described  is  lo..ate,l.  It  is  evident  that  when 
the  head  is  moved  in  any  dinrtim.  tl...  tluid  m  some  of  these 
eanals  will  be  set  in  motion.  It  is  this  nu)vm.-nt  ot  the  fiuid 
which  stimulates  the  hair  cells.  That  this  is  really  the  function 
of  the  sen.icircular  canals  is  proven  by  the  fact  that  if  they  are 
irritated  or  destroyed,  grave  disturbances  occur  in  the  bojl.ly 
movements.  This  is  what  occurs  in  Meniere's  disease,  m  which 
attacks  of  giddiness,  often  severe  enougii  to  cause  the  patient 
to  fall  and  accompanied  by  extreme  nausea,  are  the  chief  symp- 
toms   the  lesion   being  a   chronic   iuHammation   involving  the 


THE  SYMPATHETIC   NERVOl'S  SYSTEM. 


277 


Homiciri'ular  canaN  It  is  bolioved  by  some  tliat  tlif  cmistaitt 
movonioiits  of  the  Hnid  in  tho  st'iiiicircular  canals  is  tli.>  cause 
of  sea  sickness.  The  unusual  nature  of  these  movements  causes 
confusion  in  the  impressions  transmitted  to  the  cerebellum  from 
the  canals,  but  after  a  while  the  cerebellum  becomes  acc\istometi 
to  them  antl  the  sea  sickness  pas.ses  away. 

The  Sympathetic  Nervous  System. 

Along  with  the  vagus  and  one  or  two  less  prominent   cere- 
l)rospinal    nerves,    the   sympathetic    constitutes    the    iiiiliniinnif 
nervous  system,  .so  called  because  it  has  to  do  with  the  innerva- 
tion of  automatically  acting  struct\ire.s,  such  ns  the  viscera,  the 
glands  and  the  blood  vessels.     Tlie  characteristic  structural  f,-a- 
tnre  of  the  nerves  of  this  system   is  that  they  are  couuected 
witli  nerve  ganglia  located  oufsi<lr  the  central  nervous  system. 
In  these  ganglia  the  nerve  filvrs  run  to  nerve  cells,  around  which 
they  form  synapses,  thus  i)ermitting  tiie  nerve  impulse  to  pass 
on  to  the  cell,  which  then  transmits  it  to  its  destination  along  its 
own  axon    (see  p.  241).     Before  arriving    at    the    ganglion    in 
which   the    synapsis   is   formed,    the   fibers   are   called    pregai 
glionic;    after    they    leave,    they    are  called  postganglioiue.     . 
preganglionic  fiber  may  run  through  several  ganglia  before  it 
becomes  changed  to  a  postganglionic  fiber.     In  the  case  of  the 
vagus  and   other   cerebral   autonomic   nerves,   the   ganglia   are 
often  situated,  as  in  the  heart   (see  p.  IS,')),  at  the  vm\    of    the 
nerve,  but  in  the  ease  of  the  sympathetic  itself,  they  are  more 
numerous,  and  are  mainly  situated  at  tlie  sides  of  the  vertebral 
column,  where,  along  with  the  connecting  fibers,  they   form  a 
chain — the    sjimpathetie    chain — which    can    easily    be    seen    on 
opening  the  thorax  and  displacing  the  licart  and  lungs. 

Two  fine  branches  connect  each  of  the  spinal  nerves  with 
the  corresponding  sympathetic  ganglion.  It  is  through  one  of 
these  branches  that  the  sympathetic  chain  receives  its  fibers 
from  the  sjiinal  c(.r.l.  Through  the  other,  fibers  run  from  the 
ganglion  to  the  spinal  n.'rve.  Some  of  the  sympathetic  ganglia 
are  situated  at  a  -listancc  from  the  spinal  cord:  tlie  ganglia 
wi.u  h  compose  the  solar  and  hypogastric  plexu.ses  are  examples. 


278 


PHYSIOUXIY    FOR    DKNTAI.    STI  OKNT!^ 


I'   i. 


In  tlic  thoi-ax.  tlio  uppermost  jjiU'Kli""  '**  ^■'■'■>'  ^'""K''  ""'^  >** 
calltMl  til."  stillair  ijatiiiUon.  Its  pnstKaii«lionic  fiUi'rs  coiistitutf 
the  vasomotor  iii'i-v.-s  of  tlif  l)loo(l  v.'sscls  of  the  antt-riitr  fx- 
tivmitv,  aiul  th.-  s.viupatlictic  fib.Ts  to  tbt-  lu'art.  Sonu"  pn-gan- 
ttlioni.'  filxM-s  run  tlirou^'h  the  st.-llatc  ^riU'Klion  to  pass  u|)  tlic 
neck  as  th."  a  rvUal  s>n„i><'ll'<  ti<'.  th.-ir  <m"11  station  h.-iiifr  m  tlu" 
si.p.'nor  .•.-rvical  -anfrlion.  Tluy  a.-t  on  tlu-  pui)il  {dilating  itK 
on  til."  salivary  fjlaiids  (causing  vasfonstriction  aii.l  stiiimlatinn 
gla.i.lular  .•halites),  an.l  on  111."  liloo.l  v.-ss.-ls  of  th.'  Ii.'a.l,  fac" 
and  iiiuc.isa  of  tin-  insid."  of  tli."  mouth. 

From  about  th."  Hfth  .b)rsal  v.Tt.-bra  .i.)\vn\var.ls.  bran.-lics  run 
from  th."  sympatlu"ti."  .-bain  on   ."a.-h  si.h"  to  b."com."  .-oll.'.-tcd 
into  a  larK."'nfrv.'  .-all.".!  tb."  ;irnit  sphuKhnii.  wliii-h  passes  .lown 
by  th."  pillars  .)f  th."  .liapbray;m  into  th."  ab(l(mi."n  ami  runs  to 
til."  Ranglia  of  th."  .-o.-lia.-  i)h"xus.     This  iutv."  sui)!)li."s  all  of 
th."  blood  v."ss."ls  of  th."  intfstin.'s  and  oth.-r  abdominal  viscera. 
Its  action  on  tb."sc  vcss.'ls  has  altva.ly  b.-cn  .Icscribcd    (s."."  i». 
1!)1  ).     It  also  carries  n."rv.'  impuls.-s  for  the  control  of  tb."  move- 
ments of  the  st<miach  and  int.'stin.-s  an.l  for  s.»me  of  th."  dig.-stiv." 
Hbui.ls.   In  th."  ab.lom.'U  th."  sympath.'tic  chain  giv.'s  otf  branch. "s. 
which   form  tlie  P'Iriv   nrrns  an.l  supply  the  blood  v."ss."ls  .)f 
the  tower  extn-mity.     It  is  important  to  imt."  that  the  coim.-ctimis 
b."t'v."en  the  sympatlieti.-  syst.-m  and  th."  cer.'brosi)inal  axis  ar." 
limited  to  the  "spinal  nerv."  roots  bt"twe."n  th."  secoii.l  thoracic  an.l 
the  s."con«l   lumbar.     Th."   r.'sults  which    follow   stimulation   of 
th."  sympathetic  syst."m   ar."  .-xactly   lik."  tlmse   uhicli   ar."  i)ro- 
duc.'d  by  inj.-etions  of  adrenalin  ise.'  p.  1:50). 


CllAI'TKFt  XXIX. 

TllK  SIMOCIAL  SKNSES. 

Till-  sciisdry  nerve  teriiiiiiiitioiis.  or  jiffereiit  leeeptors.  tliiit 
are  scattered  over  the  skin  are  atVeeted  hy  stimuli  wliieli  eoiiie  in 
aetiial  eontaet  witli  the  surface  of  the  body.  In  order  that  tlie 
stiinili  transmitted  from  a  distane-  ,  sueh  as  those  of  lifjht.  sound 
and  smell,  or  the  pro.jieient  sensations  as  they  are  called,  nuiy 
be  appreciated  by  the  nervous  system,  specitieally  designed  or- 
fians,  called  the  organs  of  special  sense,  are  re(|uired.  Th 's.- 
organs  collect  the  stimidi  in  such  a  way  as  to  cause  them  to  act 
etfectivcly  on  recei)tors  which   have  been  esiiecially  adapti'd  to 

I'cact  to  them. 

Although   not  really  a   projicieiit  sensation,  taste  is  conven- 
iently considered  along  with  the  above. 

Vision. 

Light  is  due  to  vibration  of  the  ethereal  particles  that  oc- 
cupy space.  The  vibrations  occur  at  right  angles  to  the  rays 
of  light,  and  the.se  travel  at  high  velocity  in  straight  lines  from 
the  source  of  the  light.  The  rate  of  vibration  of  the  rays  is  not 
always  the  same,  and  on  this  ditfereuce  depends  the  color  of  the 
light,  red  light  vibrating  much  slower,  and  its  waves  being 
accordingly  much  longer,  than  those  of  violet  light.  The  termi- 
nations of  the  optic  nerve  have  been  si»ecially  ileveloped  as  the 
i-etina,  so  a.s  to  receive  the  light  waves,  lint  in  order  that  a 
comprehensive  picture  of  everything  that  is  to  be  seen  may  be 
projected  on  the  retina,  an  optical  ai)paratus,  consisting  of  the 
cornea  and  lens,  is  situated  in  front  of  it.  The  retina  and  the 
optical  apitaratus  are  built  into  a  glolu — the  eyeball — which, 
pivoting  on  the  attachment  of  the  o|)tic  nerve,  can  be  so  moved 
that  images  from  ditferent  parts  of  the  tield  of  vision  nuiy  bo 

279 


280 


PlIYSI»)Ii<H5Y   FOB  DENTAL   STIOENTS. 


fm-iiMMl  in  turn  on  tlu-  n-tina.     Th.'sc  niovomontH  arc  I'tr.rt.-d 
by  1h<>  80-i!allo(l  ooular  muscles. 

Tlicrc  arc  therefore  three  functions  involved  in  the  act  of 
scciuK:  (1)  That  of  the  retina,  in  reaetiiiK  to  li^lit.  (2)  That  of 
the  cornea,  etc..  in  focusin«  the  li^'ht.  (:5)  That  of  tlie  ocular 
muscles,  in  moving  tiie  eyeball. 

The  Optical  Apparatus  of  the  Eye. 

It  will  readily  be  s.'cn  that  the  eye  is  constructed  on  niucii 
the  same  principle  as  a  i)hoto>irai>hic  camera,  the  r.'tiiia  beiiiir 
like  the  .sensitive  plate.  There  is,  ho\vev«-r.  an  important  dif- 
ference in  the  manner  by  whidi  objects  at  varying  distances  are 
brought  to  a  focus  on  the  sensitive  surface  in  tiiese  two  cases: 
in  the  camera,  it  is  done  by  a.ljusting  the  distance  between  the 
lens  and  the  focusing  screen;  in  the  eye,  it  is  done  by  varying 
the  convexity  of  the  lens. 

In  order  to  unch-rstand  how  the  optical  apparatus  works,  it 
is  necessary  to  know  something  about    the   refraction  of  light. 
When  a  ray  of  light  i)as.ses  from  one  medium  to  another,  it  be 
.•omes  bent  or  refracted.     When  it  passes  from  air  to  water  or 
glass,  for  examide.  it  becomes  refracted  so  that  the  angle  wliieh 
the  refracted  I'ay  makes  witii  the  perpendicular  to  the  surface 
is  less  than  that  of  the  entering  ray.     In  other  words,  the  ray 
Ix'comes  bent  towards  the  perpendicular.     The  greater  the  dif- 
ference in  density  between  the  two  media,  the  greater  is  the 
diflfcrence  iH-tween  the  two  angles.    A  figuiv  expressing  the  ratio 
between  these  two  angles  is  called  the  iii(h.i-  of  r< fraction.     If 
the  ray  of  light  leaves  the  d.-nser  medium  by  a  surface  which 
is  parallel  with  that  by  which  it  entered  (as  in  passing  tiirougii 
a  pane  of  glas.s),  it  will  be  refracted  back  to  its  old  direefu.n, 
b\it  if,  as  in  a  prism,  it  leaves  the  denser  medium  by  a  surface 
which  forms  an  angle  with  that  by  which  it  entered,  the  original 
refraction  will  be  exaggerated.     If  two  prisms  be  i)laced  with 
their  broad  ends  t<.gether,  parallel  rays  of  light  coming  from  a 
certain  direction  will  be  Ix-nt  so  that,  on   leaving  the  prisms, 
thev  meet  somewhere  behind  them.    Two  prisms  so  arranged  are 
virtually   the  .same  as  a   bkonvc.r  }n,s.     It   is  plain  that  the 


VISION. 


281 


fociisiiijf  power  of  such  Ji  Ifiis  will  (Ii'ImmiiI  mi  two  things:  first 
its  index  of  refraction,  mid.  secondly    the  curvature  of  its  sur- 
faces. 

A  considerahle  part  of  the  actual  retraction  of  the  lays 
which  enter  the  eye  is  accoiiij)lislied  at  thi'  curved  surface  of 
the  cornea,  a  .smaller  def,'ree  of  refraction  takinj,'  place  at  the 
leiLS  itwlf.  The  rea.son  for  this  is  that  the  refractive  ind'X 
from  air  to  corn.  ;i  is  mucii  )jreater  than  that  between  the  lens 
and  the  humors  of  the  eye  in  which  the  lens  is  suspended,  tli  se 
humors  and  the  cornea  lia'iiiu  very  much  the  same  refract ive 
indices.  The  eiitoriiifr  '"ays  are  therefore  iifracted  at  two 
phii-es  in  the  eye.  namely,  at  the  anterior  surface  of  the  cornea 
and  on  i)a.ssiiig  through  the  lens. 


\'\H.   rrj.  —  Kiiiiiiiitidii  III'  iiniiH:!'  on   r<'tiiia.   O..I.   i.s  the  nptir  axis. 


Accommodation  of  the  Eye  for  Near  Vision. — When  the  eye 
is  at  rest,  its  optical  system  is  of  sui  n  i  strength  that  parallel 
rays.  i.  e..  rays  that  are  reflected  from  objects  at  a  distance,  are 
brought  to  a  focus  exactly  on  the  retina.  The  picture  thus 
formed  is,  liowever,  upside  down  jr.st  for  the  same  reason  that 
it  is  so  on  the  .screen  of  a  camera  (Fig.  .V2).  When  the  object 
looked  at  is  so  near  that  the  rays  reflected  from  it  are  diverge'it 
when  they  enter  the  eye,  it  becomes  neces-sjiry.  if  the  image  is 
still  to  be  focused  on  the  retina,  that  some  adjustment  take  jUace 
in  the  ojitical  system  of  the  eye.  This  could  happen  in  one  or 
two  ways,  cither  by  the  <lis1ance  between  the  lens  and  the  retina 
becoming  lengthened  (the  method  used  in  a  camera),  or  by  in- 
creasing the  convexity  of  the  Ions.     The  former  process  cannot 


2H2 


i'} 


r'llYSI<)l,(HiY    F'l»K    HKNTAI.    STIDKNTS. 


vvln.h  this  l.ul«in«  ..f  tl-  i.-.s  n...  ...  prov.-n    ?  ;;;-  ;  J  '- 

if  tlu-  ev,.  ..f  a  iHTson  who  is  l.u.k.n^'  M  s,.nu-  .l.stant  objM  t    m 
1^  U'l  fron/th..  si.i.  oMh.  h.a.lMhat  is  to  sa^^^^^ 
Ts  n,sv  to  not-  th.  .xa.-t  ,.osition  of  th.  .ns.  wh.eh.  w.th  th. 
,  pi     ,;  its  n.nt.T.  hand's  as  a  .•in-ular  ..u.ta.n  .,ust  ...  t.-o,.t  of 
.,      Vi,.  :>:»..     If  th.  1—..  is  MOW  toi.l  to  r.,ar.l  so.... 


' 


KiK.   ^3.-S...•. through  ,h.-  »"  ;;"J"  ::;!',,  ;a   the   nmrsin.  :    /-. 

tho   l..ns.   fi.  th-  .mary  >'-;"7;;^,';:^^ '"  n;:^    ,"■„,.,:..,..„.  hy  .-.  M.  spur- 
<,tU'  or  oUl.T  prot.clive  coal  ..f  th.'  iM  .      I  I 

iify. ) 

ob,..t  h.Ul  .los.  to  hi,...  it  will  h.  s....  that  th.  iris  is  p..siu.l 

forwanl  ...a.vr  to  th.  .o.-...a.    That  th.s  .s  .-.ally  .h.c  to  a  b,.l« 
r     t^.  a..t.,-io..  su.-fa..  of  th.  i...s  ca..  b.  show.,  by  ,  aeu'f 
'a,..ll.  to  o...  si.l.  a,.d  a  l.ttl.  i..  frc.t  of  th.  h.a.l  an.l  the.., 

•n,      t  ..  oth..-  si.l..   vi.wi,.,  th.   i...a,.s  of   th.   .a..cU.   «a,.,. 

1^  ;      ...  ..ast  oo  tl y..     It  will  b.  s.....  that  o...  ....a^.  oc.,... 

"  '       ;„t..,.io,.  su.fa..  of  th.  .o,-...a.  a..a  a..oth..-   l.ss  d.st....t. 

a      he     utorior  su.-face  of  th.  l...s.     This  i.,.age  f.-o.u  the  l.us 


VISION. 


283 


will  !)»'  sfcii  to  mi>vi'  forwanl— that  is  to  say.  clowr  ti»  tin-  iiiiatfi- 
at  tilt'  coriii'a — wIumi  tin-  pci'siiii  sliifts  lii.s  Kii/c  from  a  diMtaiit 
to  a  near  ohjci-t.  Wy  usiiiK  optical  apparatUH  for  iiH'a.Huriiif;  the 
si/i'  of  the  iiiia^fcs.  the  dctrrcc  to  which  the  cimvi-xity  of  the  Iciis 
has  iiicn-ascii,  as  a  result  of  the  Itiiijriiitf,  can  Im'  accuratt'ly 
Mit'asuriMl. 

This  fliaiinr  ill  the  convexity  of  the  lens  (lepcmls  on  the  fact 
that    it    is  composed   of  a   hall   of  transparent   elastic   material, 
which  is  kept  more  or  less  tiatteiied  antero-posteriorly  iM-cause  of 
its  beiii);  slun^  in  a  capsule  which  compresses  it.     The  edjjes  of 
the  capsule  arc  attached  to  a  fine  lijranient  (the  suspensory  lijfa- 
meiit),  which  runs  backwards  and  outwards  to  l>ecome  inserted 
into  the  ciliary   prm-esses   (V'm.   '>•"{).     These  processes  exist   as 
thickenings  of  the  anterior  portion  of  the  choroid,  or  pi^riiieiit 
coat  of  the  eye.  and  they  can  he  moved  forwanis  by  tiie  action 
of  a  small   faii-shai)ed  muscle,  called  the  ciliary  muscle,  which 
at  its  narrow  end  originates  in  the  coriieo-schleral  .junction,  and 
runs  back  to  Im'  attached,  by   its  wide  end,  to  the  ciliary  pro- 
cesses.    When  this  muscle  is  at  le.st.  the  ciliary  processes  lie  at 
such  a  distance  from  the  edues  of  the  lens  that  the  suspensory 
lifjament  is  i)Ut  on  the  stretch.     When  the  ciliary  ninscle  coii- 
traets,   it    pulls  the  ciliary   i)roce.s.ses   forward,   thus  slackenins? 
the  sus|)ensory  ligament  and  removinj;  the  tension  on  the  capsule 
of  the  lens,  with  the  result  tliat  the  latter  bulges  because  of  its 
elasticity.     The  ability  of  tlu'  lens  to  become  accommodated  for 
neai"   vision   depends,   therefore,   tirst.   on    the  elasticity   of  the 
len.s.  and  secondly,  on  the  ac^"         ♦"  the  ciliary  muscle.     Inter- 
ference with  either  of  these  i       '        iccommodation  faulty.     For 
example,   the  lens  along  witi.    .lU)  other  elastic   tissues  of   the 
body   |e.  n.,  the  arteries   (p.   17.">)|,  becomes  less  elastic  in  old 
aj?e,  thus  accountinj;  for  the  ■■loiifr-sightedne.ss"  (ov  presbvopia) 
which  ordinarily  develops  at  this  time.     Paralysis  *>;  the  ciliary 
muscle  produces  the  same  effect   in  even  more  marked  dejfree. 
which  explains  the  utter  inability  to  bring  about  any  accommo- 
dation after  treating  the  eye  with  atropin,  which   is  given  for 
this  i)urpo.se  before  testing  the  vision  in  onh'r  to  find  out  the 
streiigth  of  ienst's  reiiuirod  to  correct  for  errors  in  refraction. 


284 


riIYKK»l-iH}V   FOR  nr.NTAli  sTinENTfl. 


ipl 


it 


•  J- 


Th.  runction  of  the  Pupil.-Evory  optical  in-tnunont  con- 
tains n  so-calloa  .U.M.hr„„n.  which  is  a  black  curtan.  havn.K  u 
"ntral  apcrtu,-c,  who.-  .iia.nctcr  can  he  altcrd  to  "»>;-' 
size.     The  object  of  thin  is  to  prcv-nt  all  »nncceH..tv   n>s     t 
«ht  fn.n.  entering  the  optical  instr.nucnt    thus  -;•;••;«- 
..n-asinK  the  .listinctncs  of  the  ima,e.     In  the  eye   t   .s  ^  ut 
is  perfornu-d  by  the  iris  with  the  ,>up.l  n.  Us  center     Th       /^ 
.,,•    he  pupil  is  alterea  by  the  action  of  two  s^-ts  ot  nu.scle  1  be, s 
,  t!u.  iris.    One  of  these  runs  in  a  circular  n.anner  aroun.l  th 
•„„„.,  ...l«e  of  the  iris:  by  contracting  it  causes  const  net  ...n  of 
„„.  pupil.  „„  ..vent  which  ..ccurs.  alon«  with  the  buku.«  of  the 
1    iLriuK  acc«nun.Hlation  for  near  visio..    The  other  layer  of 
tibers  runs  in  a  ra.lial  n.anner.  an.l  by  contract.n«  <-au.-s  .hla- 
„,„,„  „,  ,„,  p„pi,    This  ocurs  in  partial  '^''-ij--;;;;  ;;;;',; 
..v..  .s  at  rest  (aaln.uKh  not  .luru.K  sleep,.      T'c  e.rcubu   hb  rs 
an-  supplied  bv  the  third   nerve,  and  the  ra.lnd  hbers  by  the 
sv„,pathetic.     rn.ler  ordinary  conditions  both  nu,s..les  are  n-  a 
:;ate  of  tonic  contraction  (see  p.  2.>:n.  so  that    the    actual    s./.e 
„,•  „,,  pupil  at  any  n.on.cnt  is  the  balance  between  two  opposn.fx 
,„nsc,dar  forces.    This  ren.lers  its  ad.justn.ent  in  s./.e  very  s..ns,. 
li^vo      Kor  exan.ple.  it  can  becon.e  dilated  either  by  stnnulatn.n 
of  the  svn.pathetic    (which  occurs  when   any   irritative  tumor 
..ffects  the  cervical  synipathetic  nerve),  or  by  paralysis  of  the 
third  nerve  (as  by  piviufr  atropin).     Convers.dy.  constriction  o 
the  pupil  mav  be  the  result  of  stimulation  of  the  third  nerve  (as 
by  a  tumor  at  the  base  of  the  brain)  or  paralysis  of  the  sympa- 

^''tIicsc  local  conditions  actinjr  on  the  offm  „t  nerves  to  either 
pupil  are  not  nearly  so  often  calle.l  into  play  as  conditions  actuiR 
nfli  xhj  on  both  eyes  at  the  same  time.  ^  •   . 

Certain  of  the  affe.vnt  impulses  whieh  call  these  reflexes  into 
plav  travel  by  the  optic  nerve  to  the  nerve  centers  for  the  pupil, 
such  for  example  as  the  stimulus  s.-t  up  by  liRht  talhns  on  the 
n-tii.a  The  atr.nnt  pathway  concerne.l  in  the  contraction  ot 
the  pupil,  which  occurs  in  accommodation,  mu.t.  on  the  other 
hand,  be  a  ditT.rent  one  l>ecause  in  the  .lisease  loco.notor  ataxia 
(see  p  254)    the  pupil  contracts  ou  accommodation,  but  does  not 


VISION. 


28:» 


i1<>  Sit  wlifii  li«ht  Ih  tlirowii  iii(i>  tin-  vyvs.  Tlif  iifi-vr  cfiitfi-H  for 
the  pupil  air  vfi-y  Mfiisitiv.'  to  jffinTiil  ihivouh  cuiHlitinnH.  tints 
iHM'ouiitinj^  for  tlif  ililatation  of  tli«'  pupil  wliicli  occui-h  duiiim 
fright  or  otii.-r  r. notions,  or  |>«iii.  The  pupils  iin-  contracted  in 
tlic  early  sta>?cH  of  asphyxia  or  ancsthtsia.  as  in  tlic  early  stajrcs 
of  nitrous  oxide  atiiniiiistration.  ImM  they  become  dilated  when 
the  aiiesthcNia  or  asphyxia  becomes  profound.  Their  condition 
hel[)s  to  serve  as  a  ^auKc  of  the  depth  of  anesthesia. 

Imperfections  of  Vilion.— The  ojitical  system  of  the  eye  is 
not  perfect.  Sotnt  of  thc.v  impi  rfiitloiis  <jist  in  nirii  <  >i< . 
whilst  otiiers  are  only  oecasioiml.  The  errors  in  every  eye  are 
those  known  as  speiical  and  chronuitic  a' i-rratioii.     Sphi  riirl 


i.-|p,  r.4— .4.  spherical  ali.Tiiillon.  Tlif  ni.vs  wlii.h  strikf  Hit-  M.ainiiis  nf 
the  lens  aif  IroUBlit  to  a  focus  li.li>i.-  tliosi'  .^trikiiiK  near  tlir  nritt-T.  /■'. 
Cliroiiiatic  .ilxiration.  The  ray  of  whit.-  liwht  (  H')  is  .lisscrial.il  l.v  th.- 
l.ii.s  Into  lh«-  siKMtral  c.lors,  of  n-liich  thus.-  at  thf  r.il  .'iiil  (/.')  ar.'  lint 
hriniKht  to  a  fixiw  fio  sunn  as  th...      at  tin-  vioUt  itul    (  I). 

iilxrnilioii  (FiK.-r)4),  occurs  because  the  cdijeH  of  the  lens  have 
a  higher  refractive  i)ower  than  the  center,  so  that  the  imatjc  on 
the  retiiui  is  surrounded  by  a  halo  of  overfociised  rays.  Chm- 
wtilic  ahirndion  is  due  to  the  fact  that  white  lif<lit.  on  pas.sintr 
through  the  h-ns,  suffers  some  decomiK>sitioii  into  its  constituent 
colored  rays  (the  rainbow  colors),  of  which  certain  (vi/.,  those 
towards  the  violet  end  of  the  si)ectrum)  come  to  a  focus  sooner 
than  others  (viz.,  tho«e  towards  the  red  end'),  thus  creating  a 
colored  tfdge  on  the  focused  imrge.  The.se  errors  are  greatly 
minimized,  although  not  entirely  removed,  by  the  pupil,  which 
cuts  out  the  peripheral  rays. 

The  ocamonal  errors  are  long-sightedness  or  hypennetropiji. 


286 


IMIYSloI.niiV    FOR    PFATAI.    STIOKNTS. 


i 


sl..>rt.si.rlit.-.iiirss  or  niy..l.ia.  iin.l  asti-niatisin  (  Fip.  ....>.    //.'//'"•- 

»M/ro,,/a  is  -In.  t«»  11...  ...svimll  1..m>,«  to..  sl....-1  s.,  tl.at  th.-  focus 

of  tl...  i.na«.-  is  l...iM..,l  ti>,.  ivlina.     Tl..-  .-rmr  is  .-om-.-t...!  by 
pn-scribiM-  .-onvx  ^'lass..s.     M iiopia  is  .In.'  to  tl..-  opi.os.t.'  von- 


k 


Vi^r  "r.^.-ICn-rs   in   r..fn.o.u.n  :      K  shows   th.   rormalion   of   tho   ImaRe   on 

£?'rv;;r;;;:;:;::;;rr:s:r.':r=,''v;;:rr;;":s: 

Uon   in   short-siKht,   or   mvo,.m,   wh.-re   the   ..y-hall   is   too   Ion.'. 

.lition,  that  is.  th.-  .-y..ball  is  too  lonfj.  so  that  tl..-  focus  occurs 
i„  front  of  it.  roucav.  fjlass.-s  corr.-ct  it.  Asti;,m„tuwi  is  duo  to 
tlu.  lens  ...•  crnca  bcin^r  of  unequal  curvature  ui  its  aiff.-n-nt 


VISION. 


287 


iiicridiiins.  This  causfs  tlif  rays  of  liylit  in  (»iic  plaiir  to  U- 
hroii^lit  to  a  t'liciis  Ix-forc  tliosc  in  otlitT  planes,  so  thai  tlii'  two 
hands  of  a  clock,  when  tlicy  arc  at  rifilit  antjlcs  to  cai-ii  other, 
cannot  ]>c  seen  distinctly  at  the  same  time,  althoiifrb  they  can  he 
success! v.'ly  focused.  A  certain  amount  of  astisrmatism  exists 
in  every  eye.  Itut  when  it  becomes  extreme,  it  is  necessary  to 
correct  it  by  i)resci-ibin^'  glasses  which  are  astijimatic  in  the 
o|)|)osite  meridian  to  that  of  the  eye.  Surb  •.'lasses  are  called 
cylindrical. 

Astijjnujtism  may  t)ccur  along  with  either  myopia  or  hyper- 
metropia.  and  when  any  of  these  errors  is  only  slight  in  degree, 
the  |)atieMt  may  be  able,  by  efVorts  of  accommodation,  to  over- 
come the  defect.  The  strain  thus  thrown  on  the  ciliary  muscle 
is.  however.  i|uite  connnonly  the  cause  of  severe  headache.  Tiie 
correction  of  the  errors  should  never  be  left  to  untrained  j)er- 
.sons,  but  a  proper  oculist  slioui<l  be  consulted,  since  it  is  usually 
necessary  to  give  atropin  so  that  the  acconuiiodation  may  be 
l)araly/.ed  and  the  exact  extent  of  the  error  measured.  The  use 
of  improper  glasses  may  aggravate  the  defect  of  vision  and  do 
much  more  harm  than  good. 

The  Sensory  Apparatus  of  the  Eye. 

The  Functions  of  the  Retina. — The  image  which  is  formed  on 
the  retina  by  the  optical  system  of  the  eye  sets  ujt  nerve  im- 
l)ulses  wiiich  travel  by  the  optic  nerve  to  the  visual  center  in 
the  occii)ital  lobes  of  the  cerebrum  (see  j).  2721,  where  they  are 
interpreted.  .Microsco|)ic  examination  of  the  retina  has  shown 
that  it  consists  of  several  layers  of  structures,  tlie  innermost 
being  of  tine  nerve  fibers  which  ari.se  from  an  ad.jaccnt  layer  of 
large  nerve  cells,  and  the  outermo.st  of  peculiar  rod  or  cone- 
shaped  cells,  called  the  rods  and  cones.  IJetween  the  hiyer  of 
larsrc  cells  and  the  layer  of  rods  and  cones  are  several  layers 
composed  of  other  nerve  cells  and  of  interlacements  of  the  pro- 
cesses of  cells  and  nerve  fibers.  The  rods  and  cones  are  the 
structures  acted  on  by  light,  the  other  layers  of  the  retina  i)eing 
for  the  i)urpose  of  comiecting  the  rods  and  c(uies  with  the  lai'ifc 
nerve  cells  from  which  the  fibers  of  the  innermost  layer  arise. 


288 


1MIYSI(>I,i..;Y    for    DKNTAIi    STmKNTS. 


The  filuTs  nil  conv.Tj,'.'  to  tlic  optic  disc,  wliicli  is  a  little  to  the 
insi.l,'  of  tl...  post,  i-ior  jmlc  of  tlic  cvcball.  At  this  point  the 
fibers  of  the  nerve  fiber  layer  bend  backwards  at  rifjlit  angles 
and  run  into  the  oj.tic  nerve,  thus  crowding  out  the  other  layers 
and  causing  the  .'xisten.-e  of  a  blind  spot,  which  can  be  readily 
<l,.n.onstrate.l  bv  elosin-  one  eye.  say  the  left,  an.l  with  the  other 
rcanlin.'  tiie  lett.'r   15   in   the   next   line.     Althouj?h   the   S   is 


also   distinctlv    visible   in   most    positions,   yet   if   the   book   be 
moved  towards  and  away  from  the  eye,  the  S  will  become  in- 
visible at  a  certain  distance  corresponding'  to  that  at  which  the 
ravs  from  it  aiv  impingin<i  upon  the  blind  spot.     As  we  alter 
the  distance  of  the  book  from   the  eye,  the  line  of  vision,  or 
visual  axis,  being  fixed  oil  the  B.  the   image  of  the  S  travels 
from  side  to  side  acros.s  the  inner  or  nasal  half  of  the  ivtina. 
and  at  a  certain  position  .strikes  the  optic  disc     Ordinarily  we 
are  unaware  of  the  blind  spot,  partly  because  we  have  two  eyes 
and.  the  blind  spot  being  towards  the  na.sal  side  of  each  side, 
the  image  of  an  object  does  not  fall  on  it  in  both  eyes  at  the 
sair.e  time:  and  partly  becaus.-  we  have  learned  to  disregard  it. 
The  area  or  extent  of  the  ])lind  spot  may  become  so  increased,  as 
by  excessive  smoking,  that  it  becomes  noticeable. 

At  another  portion  of  the  retina  called  the  forai  cnilralis,  all 
the  layers  become  thinned  out  except  that  of  the  rods  and  cones, 
especially  the  cones.     This,  as  we  .should  ex|)eet.  is  by  far  tiie 
most  sensitive  portion  of  the  retina,  and  is  indeed  the  portion  on 
which  we  cause  the  image  to  be  focused  when  we  desire  to  see 
an   (»b,ject  clearly.     The   remainder  of  the  retina   is  only  suffi- 
<-iently  sensitive  to  give  us  a  general  impression  of  what  we  are 
looking  at.     Thus  when  we  view  a  landscape,  we  can  see  only  a 
small   i.ortion  clearly  at  one  time,  although  we  have  a  g.-neral 
impression  of  the  whole.     The  portion  which  we  see  clearly  is 
that  which   is  focused  on  the  fovea,  and   we  keep  moving  our 
eyes  in  all  directions  so  that  every  part  of  the  landseai)e  may  in 
turn  be  pro])erly  seen.     AVe  see  with  the  fovi'a  what  the  re^t  of 
the  retina  informs  us  there  is  to  be  seen. 


VISION. 


28!) 


The  Movements  of  the  Eyeballs.— In  ortlcr  tluit  we  iiuiy  be 
.  nablcd  to  inovt-  "iir  eyes  so  iis  to  set'  objects  in  dilV'Tfiit  iiosi- 
tioiis  in  tlic  visuiil  tidd.  the  cyclmlls  iin-  |ii-ovi(lf(l  witli  six  little 
niiisfles.    four    recti   iind   two  obli(|iies.      Tliese   nniseles  are   in- 
n<i-vate(l  by  the  tliini.  fourth  and  sixth  nerves  (see  ]>.  2.')!»).    The 
images  in  the  two  eyes  cannot   of  course  fall  on  auatoniiealiy 
identical   parts  of  the  retina-,  but   they   fall  on   parts  that   are 
physiolofrically  identical.     Thus,  an  object,  say  on  the  ri^dil  of 
thi'  Held  of  vision,  will  cause  an  inias.'e  t()  fall  on  the  nasal  siile 
of  the  rijriit  retina  and  on  the  teniiioral  side  of  the  left  return. 
We  do  not,  however,  see  two  objects  because  by  ••x|>erience   we 
have  come  to  learn  that  these  are  rornsixnidiittf  pnliils  on  the 
retina'.      When   an  object   is  brou^'ht   near  to  the  eye,  tiie  two 
eyeballs  nmsl  converge  so  as  to  brin^';  ''  ■■  visual  axes  on  to  the 
corresi)ondin};   points.     This   converjrence   of  the   eyeballs  con- 
stitutes the  third  cliaUfTe  occiirriuf;  in  the  eyes  during'  acconi- 
niodation  for  near  vision,  the  other  iwo  beinfr,  as  we  have  seen. 
buljfinj,'  of  the  lens  ami  contraction  of  the  i)U|)i!      It  is  interest- 
ing; that  these  three  chanjies  are  controlled  by  the  third  nerve. 
If  anything,'  hapi)ens  to   throw  one  of  the   iniay:es  on   to  some 
other  i)ortion  of  one  retina,  double  vision   is  the  result.     This 
<M)i,(;ition  of  (liiiloiiid,  as  it  is  called,  can  be  brought  about,  vol- 
uutai'ily,  by  pressinsr  on  one  eyeball  at  the  cdf^e  of  the  eye.  or 
it  may  occur  as  a  result  of  paralysis  or  incoordinate  action  of 
one  or  more  of  the  ocular  m\iscles.     This  occurs  in  certain  in- 
to.xications,  .such  for  example,  as  iu  that   j)roduced  by  alcohol. 
Just  as  in  the  case  of  eiTors  of  refraction,  e.  ?-.  a-sti-^matism, 
slight  defiifes  of  (liplojiia  nmy  cause  symptoms  that   ari'  more 
(listre.ssinfT  than  where  marked  diplopia  exists,  because  we  try 
to  correct  for  sli^'ht  errors  and  the  etVort  causes  pain  (headache) 
and  fati^m',  whereas  with  extrenu'  errois  we  do  not  try  to  correct 
but.   instead,  we  learn  to  disregard  entirely  the   ima-ie   in  one 
eye.    When  the  incoordination  of  ocular  movement  is  pei'nuinent. 
as  when  it  is  due  to  shortening;  of  one  of  the  musci.  >^  it  is  called 
stnihisinus.    This  condition  is  usually  congenital,  and  cm  often 
be  rectified  by  surgical  operation. 
Judgments   of  Vision.— Hesides  these   purely   physiidogieal 


f 

■'  ■ 


290  |MlYSIOl,(KiY    K(.K    nENTAL    STIDKNTS. 

,,,obhMns  of  vision.  th.Mv  an-  n.any  oth.-rs   of   a    ^^yf-'r^^'^ 
osi.al  natu.v.     Sud,  for  .-xan.pL'  are  the  v.sual  judg.ne,  ts  of 
sL  distanee,  soli<lity.  and  eolor.     Judgments  of  s^u   and  <hs. 
U,na   are  dependent  on:   (D   the  six.e  of  the  retmalnnage      - 
th..  effort  of  aeeon>n,o.lation   necessary  to  obta.n  sharp  d.-ti   .- 
Hon.  and  V•^)  the  an.ount  of  ha/.e  .hich  appears  to  surround    he 
object.     Judgment    of   solulU,   depends   on    the    tact   that      u 
iniges  pro.luced  on  the  two  retin.e  are  not  exactly   fron.     1. 
sam^  point  of  view;   they   are  like  the  two  photographs  of  a 
oscopic  picture.     The  brain  on  receiving  these  two  sh^ht^v 
different  ni-tures  fuses  theni  into  one.  but  judges  the  sol.d.t.v  of 
tlie  obiec!     rom  the  difTerences  in  the  two  pictures. 

Judgments  of  coJor,  ..r  eolor  vision,  forn.s  a  subject  of  great 
complexitv.     It  apparently  depends  on  tlH'.'Xistence  in  the  re- 
tina of  three  varieties  of  cones,  one  variety  for  each  of  the  thr  e 
pnn.ary  colors.     The  prinuu-y  colors  are  red,  green  and  v.ole  ; 
,„d  bv  mixing  then,  on  the  retina  in  equal  proportions  (as  In 
rotating  a  dis<.  or  to,,  on  which  they  are  pau.ted  as  sectors     a 
sensation  of  white  results;  by  using  other  proportions  any  ot  th. 
other  colors  of  the  spectrum  n.ay  be  produced      When  one  ot 
these  primary  color  receptors  is  absent  from  the  retina,  color 
MindLs  exists.      Thus    if    the  red  or  the  green  receptors  an 
absent    the  patient  cannot  distinguish  b«4ween  red   ami  green 
lights.    Such  persons  cannot  be  employed  in  railway  or  nautic-U 
work. 


CIIAPTKH  XXX. 

THK  SI'KCIAL  SKNSKS  K'niitdi. 

Hearing. 

Like  lipht.  sound  travels  in  waves.  Imt  iint  r.s  tniiisverse  waves 
of  the  ether  tliat  fills  space,  but  as  l()Mf;itu<litiai  waves  of  con- 
(leiisatiou  and  rarefaetioii  of  the  atiuosi)here  itself.  The  niafrni- 
tude  of  these  waves  is  niueh  <;reater  and   their  rate  of  trans- 
mission nnieh  slower  than  the  waves  of  I'-jrlit :  therefore  we  see 
the  Hash  of  a  unn  lon}r  hefoi'e  we  iiear  its  sound.     The  several 
i|ualities  of  sound,  such  as  pitch,  loudness  and  (|uality  or  tind)re. 
depend  respectively  on  the   !re«iuency,  the  iuagnit\ide  and  the 
contour  of  the  waves.     Sound  waves  are  not  ai)|)reciated  by  the 
ordinary    nerve    receptors   but    only    by    those    of   the   cochlear 
division  of  the  eighth  nerve.    These  are  connected,  in  the  cochlea 
of  the  internal  ear.  with  a  highly  speciali/.ed  receptor  cai«able 
of  converting  the  .sound  waves  into  nerve  impulses.     Thr  cochha 
consists  of  a  bony  tube  wouml  two  and  one-half  times  as  a  spiral 
around    a    central    cdlumn,    u])    the    center   of    which    runs    the 
eiul    of    the    cochlear    nerve.     A    loiijritudinal    section    of    the 
cochlea    (V\^.  .')(}').  therefore  shows  us  this  spiral   tube   in  sec- 
tion   at    several    places,    and    it    is    noticed    that    there    i)ro.iects 
into  it  from  the  central  cohunn  a  ledfie  of  bone  havinj?  a  T-shaped 
^reo  margin.     From  the  lower  lij)  of  the  ('  a  mend)rane.  called 
.10  basilar  membrane,  stretches  across  the  tube  which   it   thus 
.lividcs  into  ■-    ■■  canals,  of  which  the  upper  is  again  divided  into 
two  by  another  mendu-ane  running  from  the  upper  surface  of  the 

bony  ledge. 

The  basilar  membrane  is  a  very  impoHant  part  of  the  mechan- 
ism for  reacting  to  sound  waves.    I{<'sting  on  it  is  a  peculiar  stru<' 
tui-e  called  the  Organ  of  ('.)rti  (  Fig.  .")7).  which  in  transvei'se  sec- 
tions of  the  cochlear  canal  is  seen  to  be  composed  of  two  rows  of 
long  epithelial  cells  set  up  on  end  like  the  rafters  of  a  roof,  with 

291 


2ft2 


|.|IYSI(>I-OOY    FOK    DKNTAI,    STinKNTF!. 


sl.ortor  -hair-  .-.•Us  h-.unu^  up  against  tl.nn.  ,.artu-ularly  on  th. 
si.l.  away  fnun  tl,..  .-.ntral  ....lun.n.  The  sound  vvav.-s  w'.jeh  a.-t  on 
tho  basilar  nn-n.bran..  are  transnutt.-.l  to  the  fluul  whu-l  h\hi\n 
„p,,,nnost  of  tl...  tlnvc  divisions  of  the  .-o.-hloar  lulu,  (sot  ^  i^ 
.-ii;  through  a  n..n.l.rano  coverinR  an  oval-slmped  opc.nng  (  1 . 
oval  window)  in  tl..  bony  pa.titio,.  s..parat.n«  »'."  n.t.iM.al  tr  m 
tl...  n.iddl..  ,.ar.  Aft.-r  .-..a.-LinK  tii.'  ap.-x  ..t  th.>  .•o.;l.lea  tb.-  p-ss 
thnni-h  a  s...all  ap...-t,.r..  in  tl...  basilar  n...n.bran..  u.t..  tl...  lowst 


ixteinal    au.lituiv     m.  auis  .     '•  ><,,.et.hli.jr  across  it  ami  t...-   l-:ustai'.iiai, 

canals;   .v,  cochl.a  ;    Vt.  upper  canal   o.   .ocl.l.a  ,   /  (.   lo«i' 
(Kroni  Howtlls   I'liysiolopy.) 

canal,  d.mn  wl.i.-l.  tliry  tn.v..l  to  los..  tl..M,.s..lv.-s  against  tl.o  num.- 
brane  cov..ri..g  a,.otl...r  o,,..ni..,   (tl...  '-'"''!  -•""'7\^'7;  I'! 
near  th.-  oval  win.low  i..  tl.f  san...  partition  ot  bono.  As  tlie.v  pass 
alont?  tli..s..  .-aiials  tlif  waves  .-aus..  tl...  basilar  ........bran.,  to  inoy.- 

or  vibrat...  The  vibrati,.n  atT...-ts  the  .-..Us  ..f  the  Organ  ot  (.orti. 
and  so  sets  up  n.  .v..  impulses  whieh  ar..  transinitb-d  to  the  coch- 
,,,,  „,,,,  b,  ,„eans  of  nerv,-  fibers  which  connect  with  ea^ 
of  the  main  c^'lls  of  the  Organ.    A  fine  membrane  (called  Ttc- 


lar 


n\- 


uss 

)Vt' 

I'ti. 
cb- 


KiK.    r.T 
mt'Mihi'iiMt' 


■iiipliiiMiiis; 


-KiiiKiMintiiMlic    view   i>f   the   otKMii 


if   Cuiti    ( 'I't'Stut  I  :     /».   li;isiliii 


.1.     fi.     illTK 


•I-   ami   (lUttT   roils   i>f   I'oiti 


hitir 


iKT.in\    Huwrlls    rhysidlduy.  I 


ec- 


ill 


HEARING. 


293 


torial)  rests  on  Xho  tops  ..f  tb.-  l.air  .-.'Us.  an.l  by  rul.hin«  o,.  th.^ 
;,.,,.„  tlH.y   num..   this  nuMubran..   au.n.u.nts  tb.   a.-fon   ot   tb- 

biisibir  int'inbraiic.  ,  , , 

W^  nu.st   now   .-onsbb..-  bow   tb.   soun.l   wavos  a.v   b,-ou«bt 

f,,,„,  tbe  outsule  to  tb.  oval  win.low.     Tb..  pn.na  oftb.  .a,  .    1- 

.,s  th.  sound  wav.s  tVo„.  tb.  ontsbl.  and  .hn-.ts  tb.n.  u.to  t  . 

rtcrnol  au<lUor„  n.nal.  at  tb.  inner  en.l  of  wb..b  tb.v  str,k. 

;,:^^;n;n.oftb.-.aror/... ir  ..  >.Ur '^^;-;-:  3 

stretcbed  b>os.l.v  in  an  obli.,ne  d.re.t.on.  a.ross    b.  .     al     n. 
.opposed   partly   of   Hb.rs   wbi.b    rad.at.   to   tb.   ....    o         < 
„„,„  bran,  froni  tb.  ba.ull.  of  tb.  n.allens.  a  proe.ss  ot  on,  ..f 
.     u.  itorv  ossi.l.s.  t..  wbieb  it  is  atta.b.d.     l'..eanse  of    b.s. 
!;;;rti.s;tb.  tyn,pani.  „>.n.bran..  unliU.  ^y-^^'^^-y'^^, 
H  eapabl.  of  vibratin^^  to  a  pr.at   var,.ty   ot   not.s.  and     1 
,i,„,  tions  .ans.  tb.  bandl.  of  tb.  n.all.us  to  n.ov.  n.  an.l  m 
l-..tw.en  tb.  tynM.ani.  nuMobnuu.  and  tb.  eoeld.a  .s    !u.    n  dd^^^^^ 

,;„.  or  1>,mi»nnn»  .onsistin-  of  a  .av.ty  a.ross  wlu.b  stu     l..s 
„Jon,  ossirirs  .onu>os.d  of  tbr..  sn.all  bon.s.  tb.  nn.    ..s 
t,,..  incus  and  tb.  stap.s.     U.sid.s  tbe  Ion,  pro..ss  or  ban.ll. 
aln.adv  des.rib.d.  tb.  n.all.us  consists  of  a  rounded  bead  s  t- 
uat^Mfabove  and  forn.ins  a  saddl.-sbap..l  arti.ulat.on  w,tb  tb. 
,,,,,  „f  tbe  in.us  and  a  sbort  pro..ss  wbi.b  runs  t-n.  ,us    1>^ 
l,nv  tb.  head  to  the  ant.rb.r  wall  of  tb.  tyn.panun,.     The  in.  u 
is  somewhat  like  a  bieuspbl  tooth,  the  nudleus  «'-t-^-^"  "'« 
the  crown,  and  bavin,'  two  fan,'s.  a  sbort  one  passu..  bacU.  rd 
„„,  H  Ion,  one  vertically  .lownwanls.    Tb.s  proe.ss,  at  its  lo. , . 
,.,Hl,  suddenly  bends  inwar.ls  to  fo.-n.  a  ball   and  so.ket  .on, 
with  a  stirrup-shaped  bone  (tbe  stapes),  tb.  foot  p..ce  of  wb.<-h 
is  oval  in  shape  and  fits  into  tb.  oval  window  alr.a<ly  n.ent.one.l. 
The  ossicles  act  together  as  a  bent  l.ver.  tbe  ax.s  ot  rotatum 
passing  through  the  sbo.l  process  of  tb.  n.all.us  mf.-ont  and  tb( 
hort  proce^s^f  the  i,..us  b.h.nd.     If  p.rp.nd.c.dars  be  dnuvn 
fn„n    his  axis  to  the  tips  of  the  ha..dle  ot  tb.  .na  l.us  and  the 
o  .g  process  of  tbe  incus,  it  will  be  fo.u.d  that  the    alter  is  o,.  y 
two'tlirds  the  length  of  tbe  fornu-r  (Fig.  .^8)      The  an.phnu  e 
of  moven.ent  at  the  stapes  will  th.r.for.  be  only  two-tbi.ds  of 
that  at  the  center  of  tbe  ty.ni.a.iic  n.en.braue,  but  one  and  one- 


294 


i-iivsiui.iMiY  Koit  i>i;nt\i.  STI  dknts. 


i 


hiilf  tiiius  Mn.ii«.-r.  Til.-  incivasr  in  fore.  witl.  whi.-li  tli.- 
iiiov.-m.'iits  ol'  til.'  tyiiii.aiii.-  m.-inhraii.'  aiv  conv.-y.-.l  to  the  oval 
win.low  is  still  flirt Inr  inamiiti.-.l  l.y  tl.r  fact  that  tin-  latt.-r  is 
onlv  oiu.-iw.-nti.th  th.'  si/.r  ..f  tl,.'  fornnT.  It  is  l.v  tlus.-  n.nvr- 
m.-nts  at  th.-  ..val  wiii.low  that  waws  an-  srt  up  m  tli.-  fluid 
,KM-.i|.viii«  th.'  iipiMTiiiost  in.'iiil.iaii.'ous  till).-  of  llu-  nK-lilm  aii.l 
thus  actihjr  on  the  hasilar  iii.iiil.raMr.     Th.-  tvii.|.aiii."  cavitv  or 


,,sV  in.us    .    ik-  l.Uuspi.l   ..-tin    with  ......  ,.n..v«s    (<)    at.a<h...l  «"  «•'"    '^ 

,.      h..   „tl..->    .unniiiK  ,l.,wn«Mnls  t..   ;iili.ul;.f   at    :>   m.,.1    n.   tli.' 

"■";"  >;''^.  'r  ,;::;;.'un:ua.:;..... ..,  ,„., .„..,.,...■ .k,..,..  ,..,«- 

i-ll's    I'hysi.il.iK.v  )  . 

tvn.panun,  a.-n.ss  whi.-h  tl...  .-hain  of  ossi.l.s  strffhcs  is  k.pt 
at  atn,osi.hfri«-  l-r.-ssuiv  l.y  th.  l-.shnlnnn  /./.<.  wluH,  roiMH..-ts 
it  with  thf  posterior  iiarcs. 

Ihafmss  m,i!i  hi   <hi<    I"  II"  followini,  oni.sts: 

\      Ktipt'in'  of  till'  tviupaiiif  iiifiiihraiif. 

•J.     Ankylosis  or  stinVnin^'  of  tl..-  joints  h.-tw.-.-n  th»-  osMcl.-s 


TtIK    SKN>K   oK   T.wri:. 


2!».') 


of 

III' 

w- 


pt 

rts 


IfS 


ati.l  th.-  li>r..i...-nts  wl.i<-h   hol.l  th.-m   ii.   plan-  in  tli.-  tvnipain.' 
ravitv      Fl.'xihilitv  of  tlu-  joints  U\vi,vu  Wu-  ossw1,.h  pn-vontii 
su.l.i;n  jars  at  th.'  oval  win.low.  for  tl..-  joint  iM-tw^.n  tin-  mal- 
leus an.i  incus.  Wmg  sa.l.ll.-.Hliap.-.l.  unl.H.ks  whcncv..,-  ahnorn.al 
„r  ..xn-sHivo  niov.MM.-nts  aiv  trans.nitt.-.l  to  tin-  u.all.'us. 

:{      IMockinK   of   tlu-    Kusta.-I.ian    tuU'.      Tl.is    is   .,uit.-   .-om- 
n.onlv  a  ivHult  of  a.l.-noi.ls  or  it  may  !«■  .in.-  sin.plv  f.  a  .atarrh 
of  th".'  tul).-.     Tl..'  n-sult  of  tl...  l.i.M-l<  is  that  tlir  p.vssu.v  <.n  tin- 
tvn.pani.-  cavitv  tails  h.-low  that  of  th.-  atmosph.-n-,  iH-caus.-  of 
absorption  of  oxygen  into  th.-  hloo.l.  an.l  tin-  ty.npan..-   n..-.M- 
bram>  bulges  inwanls  an.l  b.-.-on..-s  str.-t.-h.-.<  s..  that  it  .-annot 
vibrat.  iToptTlv  to  th.-  sonn.i  wav.-s.     '•„..  .l.-afn.-ss  ...  th.s  .-as.- 
is  .-asilv  .vinov.-.l  by  r.-op.-ninj.'  tl..-  Knsta.-hia..  tnlM-  by  l...y...tf 
air  into  it      This  .-a.,  b,-  .Ion.-  by  atta.-l.i..^  a  la.-^'.-  sy....n.-  In.lb 

to  o...   ..ost.-il.  .-losi-.K  th..  oth.-r  ..ost.-il.  a,..l  whil.-  th.-  pat..-..t  .s 

swallowinn  a  .....utl.ful  of  wat.-r.  s...l.l.-..ly  .•on.l.r.-ss.njt  th.-  b..lb. 

Th..  a.i.lit..rv  .listivss  whirl,   is  ..xp..ri..n<....l  hy  a  i-.-i-s....  on 

«oinK  i..to  con.p.-.-s.s.-.l  ai.-  (as  i.,to  a  .-aisson)   is  also  .1...-  t,.  .lis- 
t„rb.n....  in  th.-  ty...pani..  p.vss..n-.  for  it  tak.-s  a  f.w  ............  s 

b..fo.-.-  this  r.'a..h..s  that  ....  th,-  ontsi.l.-.    lil..wi..g  tl..-  ..os-  UM.ally 

r..i..ov..s  tl...  <list..».ss. 

In  all  tl..'s..  .'on.litions.  th.-  pati.-..t   h.ars  p.rt.-.-tly   wh.-n  a 
tunin,?  fork  is  appli.-.l  to  th.-  sk..ll  or  t....th.    This  is  b.-.-ans..  tl... 

SO.M..I  vibratio..s  an-  th.-..  t,.a..s...itt...l  to  th.-  .-o.-hh-a  through 
th..  bon.-s  of  tl...  I...a.l.     Wh.-n  th,-  (•...•hl..a  is  .hs..as...l    l...w.-v..r, 
th..  tuning  fo.-k  can  1...  I...a,-.l.  ....ith..r  xvh.-..  it  is  soun.l...l  m  a.r 

„or  when  it  is  applic.i  to  th.-  sk.ill  or  t.-.-th. 
The  Sense  of  Taste. 
Sci.tt.-.v,l  ov.-r  th.-  .....cons  ...c.bra...-  of  th.-  t....nu..  a...l  bu.-.-al 

c-avitv.  a...l  cxtc...ling  back  into  the  i.ha.-y..x  a...l  .-v.-..  ...to  the 

l„rv,;x.  arc  the  na.lors  of  tasL.or  lasl.   fu.ls.    T  ...y  an-  .....s 

,.„;„.M-ous  i..  the  K.-OOV..S  an.,....l   tl..-  ci.-.-u...vallat.-   pap.lhe  . 

tbe  root  of  th.-  tong..e.  a...l   i..  the   fu..j:.to.-...   pap.lhe.      l-..el 
t-.ste  bua  is  C0...P0S.-.1  of  a  ...ass  of  f..sif..r...  .-ells  pa.-k.-.l  l.ke  a 

barn-1  fiUe.l  with  stav.-s.     The  stav..s  i..  the  .-.-..t.-.-  p.-o.,e<-     as 
hai.-s  bevon.l  thos.  on  the  outside,  a-.d  it  is  ev.dc.tly  by  act..... 


m 

i 


2!Mi 


|'IIVS|.iI.<n;V    KOU   I>K\T.M.   !«TII>KNTS. 


on  tl.rsr  l.airH  tlut  .•.rtain  .iiss.,lv,.l  sul.st. s  n.-t  ii|>  a  sUmu\m 

of  t..Ht...  This  stimulus  is  llMt.  n.nvv...|  l.y  tine  n.Tvv  til.rrs 
whi.-l,  arboriz.-  arou.nl  tl..  tast-  .•.Us.  t..  tl-  .-in.r.la  ty.npan.  ami 
linjrual  n.TVs  in  it...  ai.t.imr  p.M-ti..n  ..f  th.-  t.m>ru..  an.l  tin- 
jfl.Hso|.harvn>r..al   i..  th..  ,M.st...i..r  part,     Tl.n.UKl.  th.-s.  u.-rvs 

tl,..  s..ns«ti«..H  an-  .-arri.-.l  I.,  t Mnnl.i 1  alV..r..nt   nu.-l.us  ol 

th..  fifth  an.l  ninth  n.-rv.'s  in  tli.  m..iulla  ol.l..nj:ata  .  s.-.-  1- itf. 
5!)). 


%^tn\ttiiAV^ 


<\ '[^rrowni.  '\\ 


\.',K     .v.. -S,h,..na    to    show    111.-    .•ours,-    of    Ih..    tMSt.-    tib.TS    (>   .,n    U.w^u,-    to 

i„«-s  o.,s,.,va.ioi,s.      TlM-   ftiU   bla.'k   H...-S    nnlirat..   M.,...l..r   path    l.>    « .1.. 

i„„,uls,.s    n.ay    .va.-l,    tl..-    i..aii,.       .  K....n    H..w.ns    l-hys.olosy.) 

Suhslancfs  .-annot  hv  tastcl  unh'ss  tii.'.v  arc  in  soluti...!.  Iluis. 
,|„i„i,„.  pow.l.r  is  tastcl.'ss.  On.'  nf  tli.'  functions  ..f  saliva  is 
to  britif:  suhstanc-s  into  s..lntion   in   nnl.'r   Unit    tti..y   may    i... 

tasted. 

Th.MV  an-  f.uir  fumlamcntal  tast..  sensations:  sweet,  saline, 
bitter  ami  sour  ..r  aei.l.  The  ability  to  .listin-uish  .'aeh  of  th.'s.- 
tast.-s  is  not  ewnly  .listribut.-.i  owr  tlie  ton^'ii.-,  but  oeeurs  in 
.letiuite  areas  whieli  can  be  inai-iM..!  ..ut  by  api.lying  solnlion.^, 


TT 


.^ifU 


TIIK    SKNSK   OK   TAVrK. 


21)7 


poMMcssiiiK  oiu'  or  otlirr  of  tln'Nc  tiistt'S,  liy  mfiiiis  of  ii  fiin-  ••miifl- 
Imir  hniHli  to  diffcri'iit  portions  of  tin-  tonjruc,  iiftir  <liyiiiK  fliis 
somowhat  with  h  towtl.  lUtttr  taste  in  al)s<iit  from  all  parts  of 
tho  toiiRiK'  t'XcM'pt  tfn-  liasc.  hciu'f  a  mouthful  of  a  wt-ak  solution 
of  (|uiniin'  sulphate  has  inactieally  no  taste  until  it  is  swal 
lowed,  when  however,  if  tastts  intensely  hitter.  Swe.t  and  .viur 
tHMti'M  are  nioNt  aeute  at  the  tip  and  sides  of  tin'  tonnui'.  Saline 
taste  is  more  evenly  distrihiited. 

This  liinitioH  of  Iti.sit  St  n.s((li<iits  is  not  a  hard  and  fast  one. 
for  nciKhhoriuK  taste  hutls  in,  say.  the  hitter  an-a  at  the  root  of 
the  tonjjue  may  appn -inte  ditferent  tastes;  thus,  if  a  solution 
eontainiii'y  i|uinine  and  suyar  he  a|«plied  to  one  pai)illa.  it  may 
taste  sweet,  whereas  when  applied  to  a  nei^'idK)rin<r  one.  it  tastes 
hitter.  With  weak  solutions  one  taste  may  neutralize  another: 
thus  the  addition  of  a  small  amount  of  salt  to  a  weak  sujrar  solu 
tion  may  remove  its  sweet  tasti-.  This  neutrali/atiun  of  oin' 
taste  by  another  does  not  occur  when  the  solutions  are  sfronjfer; 
thus  a  mi.\tui'e  of  acid  and  sujrar.  as  in  lemonade,  causis  stinni- 
latioii  of  lM)th  "acid"  and  "sweet"  taste  huds.  The  stimida- 
tion  of  one  kind  of  ta.ste  bud  may  cause  other  taste  buds  to  be 
eomo  nmre  acutely  .sensitive,  which  ex|)lains  the  sweetish  taste  of 
water  after  washing  out  the  mouth  with  a  solution  of  salt. 

Attemjjts  have  been  made  to  correlate  '/"  ihiniiml  slnirliin 
of  orffdiiic  siibstmici  s  irilh  tin  Insfi  which  they  excite,  but  with 
little  success.  Thiw  pure  proteins  have  very  little  taste,  whereas 
half-digested  protein  is  intensely  bitter;  on  the  other  hand,  the 
|»ure  amino  acids,  which  form  a  larjfe  pi-oportion  of  the  de- 
composition products  in  such  a  di^rest.  are  sweet.  In  I  he  case  of 
acids  and  alkalies,  however,  it  lias  been  established  that  tiie  aeitl 
tas*e  is  due  to  the  Il-ion  and  the  alkaline  to  the  Oli-ion.  Soine 
acids,  .such  as  acetic,  ta.ste  more  acid  than  we  should  expect  from 
their  defire*'  of  dis.sociation  into  ll-ioiis.  This  is  because  of 
their  power  of  penetration  into  the  cells  of  the  taste  buds.  When 
l)latinum  terndnals  from  a  battery  are  applied  to  the  tonj^ui  , 
the  positive  i)ole  tastes  alkaline  and  the  nef»ative  acid,  because 
Oll-ions  accumulate  at  the  former  and  H-ions  at  the  latter. 
Association  I'.ktwkkx  Taste.  Torrii   and  SMKi.t,. — I'>ut  f'  >■ 


2<»8  |'HYSl(lI.<HiY    FOR   DENTAL   STVDENTS. 

Unn-  fu,ulanu.ntal  tastos  .lo  not  nearly  represent  all  the  teste. 

,.a  flavors  with  whieh  we  are  fan.iliar     The  rehsh  o^  a  ^s 

n.....l    the  nmuanev  of  eondinients,  the  hou.iuet  ot  d  hm  '«nu, 

are  involved,  namely  (D,  tnosi  oi  hm" 

,.,.e  of  aei.ls    thus  a.hling  an  astringent  eharaeter  to  the    sour 
:l     ud    '>    those  of  sn.ell  as  in  the  ease  of  wnies  ami  flavored 
fi;  ;      The    n  Portane,.  of  the  sense  of  smell  in  "ta-st.n.     ex- 
it th     loss  of  this  ability  during  nasal  eatarrh  or  cold  n 
It;  Wad      l"  der  sueh  conditions  an  apple  and  an  on.on  may 

''t:!^\ir,„s  when  applied  to  the  tongue  ^^^^ ^^^J^^^^ 

•      vtr  .,,...♦  ,l..ffrees      Thus  cocaine  tirst  ot  all  pdrai\/.<s 

;;:;;;;,;^  :    ct^ion   sensation  so  that  pam  is  no  longer 

^  t    m      n  acid  loses  all  of  its  astringent  ..uaht.es  and  nu.e^ 

1  \  little  liter  the  hitter  taste  also  disappears,  then 

:;'i,:;;::on;"i«'i:ii"^«»..' -■-"»•-■■■"'''■■■,•'•■ '■°™''''' 

,     ■,        ,  °  ,1  its  Ml  ..ffcet.     Another  i„f.r..ti„s  .  rur  acting 

s;;;;'z,:ri..."n:o:  «r  :■.  ...„  or  »„»»,„., >■ 

«.„««tio„  (a,trhw...<-.v.  .<•:)  Wins.  l.o.vv..r,  unaff....,-.!. 
The  Senae  of  Smell. 
I„  ,„„„  tl,,-  s,„s,.  of  smoll  »  v,.,-.v  f..l.l.-  W1.-1I  c-oi,.l.an.l  will. 

.,iff,,«,t  ■n.livi.ln.l..    It  is.  n.on.ov..,-.  .v».i,l    fat.g .     .  t^ 

i:  r.":   ;:;';,:;  if  a  t^-ifta,  i.,..*. ^v, ,nvi,..  ^. 

bulb.    After  making  conmH-tions  witli  nerve  cells  here,  the  path 


THE   SENSE   (IP   SMEIiL. 


299 


wav  is  coutiinu'd  along  tli."  olfactory  tract  to  tlu"  hii)pof'aini>al  • 
ri-f^'ion  of  the  brain.     As  wc  would  oxpcct.  this  portion  of  tli.- 
brain  is  much  developed  in  these  animals  having  a  very  acute 

sense  of  smell.  . 

The  olfactory  ei)ithelium  is  kept  constantly  moist  with  fluid 
and  substances  cam.ot  be  smelle.l  unless  the  odorous  particl.'s 
wiiich  they  give  off  become  dissolved  in  this  fluid.  These  odor- 
ous particles  diffuse  into  the  upper  nares  from  the  air  curi-ents 
wliich,  with  each  respiration,  are  passing  backwards  and  for- 
wards along  the  lower  nasal  i)assages.  There  is  no  actual  move- 
ment of  air  over  the  olfactory  epithelium. 

Xatikk  (»k  Stimilcs.— It  is  impossible  to  state  just  exactly 
wliat  it  is  that  emanates  from  an  odorous  body  to  excite  the  ol- 
factory si'nse.     All  we  can  say  is  that  it  does  not  reciuirc  to  be 
present  in  more  th«n  the  merest  traces  in  the  air  in  order  to  un- 
fold its  action.    Thus  even  in  the  case  of  man,  with  liis  undevel- 
oped sense  of  smell,  0.000.000,000.04  of  a  gramme  of  mercaptaii. 
suspended  in  a  litr."  of  air.  can  be  smelled.  ami  in  the  case  of  the 
dog.  the  dilution  may  no  doubt.be  many  thousand  times  greater. 
The  sense  of  smell  is  th.'  most  important  of  the  projicient  sensa- 
tions in  certain  aciuatic  animals,  and  is  very  closely  associate<l 
with  the  sexual  fiuictions  of  the  animal.    Just  as  in  the  case  of 
taste,  certain  substances  owe  their  peculiar  odors  to  simultam-- 
ous  stimulation  of  the  olfactory  epithelium  and  the  receptors  of 
common  .sensation.     Thus  the  pungency  of  acids,  of  ammonia, 
chlorine,  etc.,  is  due  to  stimulation  of  the  endings  of  the  fifth 
nerve.     Attempts  have  been  made  to  classify  odors,  as  has  been 
done  for  tastes,  but  with  no  .success. 


CIIAPTEH  XXXI. 
TllH  Ml-SCTLAR  SYSTEM. 
The  General  Properties  of  Muscular  Tissues.-TlR.  iulinu.t. 

s,„.  Jm  ;..luT  f„n,„  or  .!-..■  i»  tl»'<  »«  '""'■:;'';,,.,  Vli 

;::,i;;:';ir,r:»  :;:..■■  t...  .,...,.„.;.,..,.,  i,, ,;.... ^.« 

,.,„,  ;„  „„.  ."."-v-^»;  .1;;  ■■■''■  ^^;.,\i „,„., „„. 

„„„  „,„„„„„  „,  »,„o  ....>•»  <^^  r ':;  ;;,r:  ;i;;. 

vnis  sv'st.-ni  acting  on  another  property  ot  nmsele.  -anu-lN    its 

•■•-r'''f/v:;:;;r;::t 

■•"■r::ti  :H,,!";:u.n;:;'io..  ot ,».,,.  ot » t,,«  ,„»,■  .,o  „,„.,. 

,,;  .".  s    g      .,,,,1  .,.».-lnnR  o„o  ,.,,,1  .0  a  sui.aH.:  ■  a,„„  no,    .    ■ 

f  l,d    a  .  n»olc  b»  olitrically  .K.-it,.!,  it  will  mor,l  ,1,  e.,.,- 
JLclTo,'  L  :  ™,-v,.  on  tho  smokod  surface  ot  ,i,o  papor.  »...!  *ow 

300 


TlIK,  MlsriliAK   SYSTF.M. 


301 


1.  nuinbcr  of  iiit.'resting  details  as  to  the  properties  of  eontraetinp 

imiseles. 

The  muscle  iloes  not  begin  to  contrmt  at  tl>e  exact  moment  that 
tlie  stimulus  is  applied.  A  very  short  latent  period  (.01  sec.) 
elapses  between  the  stinndus  and  the  beginning  of  the  contrac- 
tion. During  this  time  llie  iiuiscle  is  undergoing  some  internal 
change  which  must  precede  the  contraction.  The  period  of  active 
contraction  is  relatively  short  (.04  sec.)  and  the  period  of  relax- 
ation somewhat  longer  (.05  sec).  The  ordinary  movements  ot 
the  body  cannot  obviously  be  of  the  nature  of  a  single  muscular 
contrj'  for  they  much  exceed  one-tenth  of  a  second  in  dura- 

tion. .  re  in  "fact  produced  by  a  prolonged  contraction  of 

inuscl.  -  d  by  the  fusions  of  several  single  contractions.  This 

is  known  as  idank  contmcilon,  and  it  can  easily  be  produce,! 
in  the  muscle  preparation  described  above  by  giving  it  a  seri.-s 
of  electrical  stimuli   from   an   induction   coil.     If   the   .stimuli 
be  properly  timed,  a  contraction  curve  somewhat  higher  and 
showing  no  relaxation  phase  will  be  prmluced.     When  the  ex- 
citation is  di.scontimied.  the  mu.scle  returns  to  its  normal  length. 
Tlu-  amount  of  load  which  the  muscle  lifts  has  a  peculiar  effect. 
I'p  to  a  certain  point  an  increase  in  the  load  increas*>s  the  effi- 
ciency of  the  nnisde  and  the  nmscle  will  actually  perform  more 
work  with  a  moderate  load  than  with  no  load  at  all.     After  a 
certain  load  is  reached,  the  efficiency  of  the  muscle  begins  to 
diminish  and  further  increase  of  the  load  decreases  the  work 
accomplished  by  the  nuisde.    The  principle  involved  here  is  made 
use  of  by  fork  and  shovel  manufacturers,   who   are   careful   to 
make  their  implements  carry  the  load  best  suited  to  develop  the 
maximal  efficiency  of  the  muscles  of  a  normal  average  man.     Al- 
lowing the  laborer  to  chooSi>  his  own  shovel  is  not  always  the 
best  for  the  .aborer  or  for  his  employer. 

Another  interesting  fact  is  that  a  contracted  muscle  is  more 
ihtitk  than  a  relaxed  nuisde.  E<iual  weights  attached  to  a  con- 
tracted and  to  a  relaxed  inusde  will  produce  a  greater  elonga- 
tion in  the  contracted  than  in  the  relaxed  musde.  It  is  this  prop- 
erty which  protects  the  musde  from  sudden  rupture  when  at- 
tempts are  made  to  lift  loads  that  are  too  heavy. 


y    f     ' 


:{02  IMIYSIOUWY    FOR    nENTM-    STIOENTS. 

The  Chemical  Changes  Which  Accompany  M-cular  C-t^^^^^^^ 

.uuscular  energy.    •'»^\»^;    1  ^^  ';";f,.,t  an.oiu.t  of  oxygen  is 
bnnuii      llnriiiB  imiscular  aetiMt\   a  f,n<ii  •» 

ri':i:':r;;;;sr;::::.n;t::r::n>-.-,r.,„^ 

with  energy,  so  to  speak,  (lunn. 
eause  tl.ey  have  beei.n.e  deprive.!  of  oxygen. 


CHAPiKR  XXXII. 

KKPUODICTION. 

TlH-  most  iniportin.t  function  of  an  AumnxVA  lifo  is  the  produc- 
tion of  a  new  imlivi.lual  which  in  all  peculiarities  of  function  and 
structure  is  essentially  like  the  parent.  The  fundamental  prob- 
lems of  the  proc'ss  of  repro<luction  which  are  of  physiological 
importance,  are  those  of  fertilization  and  here.lity.  Fertiliza 
tion  consists  in  the  unicm  of  two  parent  cells  to  produce  a  new 
cell  which  is  endowe.1  with  the  power  of  growth  and  subdivision. 
Heredity  refers  to  the  phenomenon  which  directs  the  cell  thus 
fertilize*!  to  develop  into  an  individual  like  its  parents. 

Since  up  to  the  prest'iit  time  most  of  our  knowleilge  of  these 
prm'csses  is  based  on  anatomical  data,  we  will  .lis(Hiss  them  very 
brietlv  and  will  pav  more  attention  to  what  we  may  term  the 
accessory  phenomena  of  rc|.roduction.  which  ar.'  of  inor.'  practi- 
cal interest  at  i)resent. 

Repro<luction  in  the  unicellular  animals  is  a  simple  process 
The  parent  cell  divides  exactly  in  halves  and  two  daughter  cells 
are  pro<luced.  In  the  multicellular  animals  this  type  of  repro- 
duction is  impossible  and  the  process  is  delegated  to  a  portion 
of  tlu  animars  body  known  as  the  reproductiv.'  system.  This 
system  in  man  includes  the  specialized  tissues  which  produce  the 
cells  or  eggs  from  which  the  new  in<lividual  develops,  and  tin- 
accessory  organs  which  are  concerned  in  providing  favorabU- 
conditions  for  the  development  of  these  cells. 

Fertilization.— A  v.-ry  simph-  tyi)c  of  fertilization  is  seen  in 
unicel:u!ar  animals,  which  ordinarily  reproduce  by  simple  divi- 
sion. After  a  series  of  simple  divisions  the  cell  becomes  uiiabl.' 
to  develop  more  cells  until  after  it  has  united  with  another  c<-ll 
to  form  one  large  cell.  This  process  is  termed  conjuw'Hon.  In 
higher  forms,  the  development  of  the  egg  is  always  preceded  by 
the  phenomenon  of  fcrtilwition,  which  is  somewhat  similar  to 

SOS 


304 


1'11YS1<)I.(KIY    FOIJ    I»I:NT.\1.    STlDKNTii. 


tl.at  ..f  .•..Miu,'ati..n  in  low.r  forn.s.     In  tins  ,.m-ss.  ..■Us  of  tw.. 
;.p..s  an.  .-,.u....rM...i.  rh.  n.nl...  .»•  sp..rn.  n-11.  or  sp.nnat  cw»on. 

Tlic  s|)friiiatozoon  lias  tlif  alnin> 


The  miflfar  clfniciits  of 


and  the  tVnialc  c'll  or  ovum, 
to  moNT  an.l  1o  p.-n.^trat."  th.'  ovum, 
botl.  MU  unit.,  t..  forn.  a  u..w  nu.-l..us,  wlu.-l.  .s  then  .-apa  .U   ot 
un.l..r,.>in,r  a  \ou;  s-.ri.-s  of  sub.livisi..ns.     In  <•  han^.-s  wlu.-l.  p.v- 
,,,1..  f..rtili/ation.  tl...  uu.-l..ar  mat.-rial  ori.Mnaliy  pn-s.-nt  m  l.otl. 
„„,..  ,„.,  f..,nal..  -..lis  is  r...lu.....l.  an.l  wh..n  ti,.;  .-.lis  tus...  t  ..■  r.- 
sultin-  nucl..us  .-.mtains  a  n.>rmal  quantity  ot  uu.-l.-ar  matnial. 
The  Accessory  Phenomena  of  Reproduction  in  Man. 
Tl...  lH.-iMninu  of  tlu'  a.-tiv..  s...xual  litV  in  n.a..  is  b.-tw-.-n  th. 
,...s  of  f..urt....n  an.l  sixt....n.  an.l  is  .-all...!  tlu-  a,'.-  .>t  pub-rty 
i:,  b..tl.  bovs  an.l  V'irls  th..  whol..  b.xly  -bows  a  nuu.k...l  .l."v..l..p- 
,„.,„t  at  tbis  tin....     Tl.e  Knmtb  of  bai.'  on  tbe  pub.e  r.-g.ons  a,..l 
,,,,.  pits,  a...l  .m  tl...  fa....  of  b..ys.  tb.-  .b...p..n.n^'  of  tb..  n.al.. 
v.,b....  an.l  tl...  .l..v..loi.n...nt  ..f  tl...  br..asts  i,.  tl..-  t..n.al..    an-  al 
,.,,.,„pa„yin,^  plu.non...na  of  tl...  ,b.v..l..p,......t  ot  P'''-'^.- 

,.,.,.,ab.s  tl...  a...  is  n.ark...l  by  tb..  -'-V;\'''7'f '"""^'r-,:    .", 
...nsists  of  a  p.-rbuli.-  tlow  ..f  n.m-us  a>..l  bl.,.,.l  tr.m.  tb.  ut...  ..s 
Tb..  ti.>w  lasts  fr.....  four  to  five  .lays,  a.i.l  r..cu..s  w.tb  -r.-at  r.-s,'..- 
la,.itv  about  ..v..ry  f..ur  w....ks.     In  ...al..s  fu^X  t'orn-.^l  s..nuna 
tlui.l.  ontainin^  liv..  sp..rm  e.-lls,  is  s..,.r..t...l.  an.l  en.etu.ns  ot  tb. 

ocnis  (X'.'ur. 

The  Female  Organs  of  Rcproduction.-Tbese  ar.^  tb.^  ovari.s. 
ovi.lucts.  ,.t..rus  an.l  tb.-  vagina.    Tl..-  ovaries  ar.-  pair.-.l  bo.l..-s 
Ivin,.  in  tl..^  low..r  part  of  tl.e  ab.lon.inal  cavity  am   held  ui  p..s,- 
tion  by  the  broa.l  ligament.     The  eells  from  wlneb  tb..  ova  d.- 
v.-b.p  are  imbe.l.le.1  in  the  fibrous  tissue  of  the  ovary     A  numb., 
of  tl  .^s..  eells,  better  .level.>ped  than  their  f..llows,  and  surn.uii.l...l 
bv  a  lav..r  ..f  cells,  whieh  f.,rm  a  sort  of  follicle,  he  near    h..  su.- 
fa,.,  ot- tl...  ova,.y.    Th....  are  tb..  araafion  foIM..,  ni  wbu-h    1... 
ova  .1..V..10P  till  th..y  are  rip...  when  tb..y  are  extru.l.-.l  into  th.- 
abdominal  cavity  by  rupture  .,f  the  follicle.    In  v..ry  ^-^o- ''PI- 
sition  to  the  ovari..s  is  a  tul>e.  the  oviduct,  whu-h  lead    t^>      - 
uterus.    The  outer  end  of  this  tube  is  fimbriated,  and  it  is  t    i- 
nished  with  cilia,  the  movements  of  which  cause  currents  m  the 


i;KI'm'l"<"'"'"^'- 


:'.'.)' 


Hauls  of  th..MlHlon,inar.-avity.  and  wl.i.-h  .InvH  tW  ova  -b  - 
:Un..nnlu.iolli.-l.-  into  tin.  ovi.l,u.t.  T'-'l^'—  -J  -  " 
s  M.l  or.....  with  ...us..ular  walls,  it  is  about  ..•..,  ...  1.-..'11. 
'       l;:;sonu.up,K.rdilat..po.1ion...alU..lt..^ 

,,  ,,,,,  ,.o„stn.-t...l  portio...  .-all-.l  th.  <-..-v.x.     M..  ••.-v.x  op 

..s,.u.llap..,-tu.vi..totl...va.i,.a.wl.i..l..s  a  .......  ~^ 

,;,„„„  u)  .M...  lo..,'  .■xt....li...'  to  th..  va,..,al  outlet  at  th.  .  NtM,.al 

"■^ILe  Organs  of  Generation  a.v  tl..  t..sti..l..s  -s  .||-1V';-- 
s....i..al  v..si..l..s.  tl..-  ..'■..is,  tW  p.-ostat..  ,^la...l.  a...l  ..  ,,u,..l... 

sL.all  t;laii.ls  aloi.n  tl.c  ...vtl.ra.  ,     ,  ■  ,    :        Unl.n- 

Tlu  t.-sti.-l.-s  ,.,>..sist  of  two  pa.-ts.  a  port.o..  ot  wh.-l.  .s     "l  .   ■. 
,„a  is  .on.-...  ...a  in  tl...  .i..v..lop.......t  of  tl...  sp-n.-ato/...     a...l  . 

:  ;::  ..all....  tl...  ..pi.n.lyn.is.  ..ontaini...  ti...  1..W...  po.^^ 

lu-  v.rv  1....^'  a,..l  .■o..v..l..t...l  .lu-t.  tl...  vas  .l.-t.-.v  .s      Fh.s    1  . 
on.  ..^"s  tl...  t..sti.-l..s  with  tl...  s,„.i..al  v.-si.-l-.s.  wln.-h  h.-  a    tl.  ■ 
r  ,    t       l>l-ia...-  .....1  i..  -los..  .vlatio..  to  tl...  pn^stat..  .la...l. 
•::..     alv..si,.l..sa,-,.....it...ll.yasl..u-t.h.-tw.tlnl....u...lu.., 

ri;i.ristl....>utMto..tl.....x.-...t..>..s..fl...tl.tl...k..l,...ya...ltl... 

'■Th!''sp......,ato.oa  a,...  .l..v..lop...l  i..  th.  t..sti.-U;s  a,..l  Hud  th..ir 

.a V  to    1...  s..n.i..al  v.-sh-Ls  through  tl..>  vas  d.-t.-.-..-.^.     ••     tl  . 
.,;-  th..v  b.ro.....  iuix...l  with  a  nu,..l...r  ..f  fliu.l  s...-,-.;t u.ns.  th. 

tf  o    whi.h  an.  a..riv..l  f.-o...  tl...  s....inal  v.s..l..s  ot  tl..-  pn-s- 

;.;;:, ;:n.l  a,..l  or  tl..-  .lan.is  .,f  Cnvp..,-.     Tl...  n-s,.lt,n«  ....xt.u-. 

is  th.'  seminal  fl.ii.l.  ...  ,   .„.., 

Impregnation.-Tl..  s...„inal  «u,.l  ...nta.n.n^  th.  sp.-n.  ato/oa 
is  a^l  in  th.^  va.i..a  .luvin,  .-.>itus.     Att.-a.t.-.l  hy  tlu-  a.  .1 
,.-,..tL  .>f  th.  s......tions  of  th..  ut..-us  or  u.ul.-..  a..  ....known  ...- 

tt     n  0    th..  sp.-r,nMozoa  soo..  .-..t..-  th.-  ut.-rin.-  -av.ty  thn.... h 

ftl  rPui,.,  i.lto  tl...  vagina.  a,..l  ti,..l  th.-i,-  way  to  tl...  ov..l...t. 
wh......  th.v  .-.Mnai..  waiting'  f..r  th.'  ..vu.n  to  app..ar. 

;^latK,n.-At  a  .out  th.'  ti,n.'  of  a  ......st.-.w.l  p..-.o.    an  ovu.n 

is  .lis..ha..,.'.l  fm..   .  rip.n...l  (J.-aatia,.  UAWU-  a...    t-'l^  ^^  - 
into  th..  ovi.hu't  hy  way  of  tl..'  fi...b,..at...l  ..xt.......ty  .jt    h    tu  . 

o\vM  whi.h  it  is  .0  ..lu.t...l  t..  th.'  ut.rus.     It  .s  a  .l.hat...l  MU.s- 
?^    ^  o  what  th.  .  xa.t  r..latiou  b.tw.....  n....st..uatu,n  an.l  ovu- 


;{06 


I'I1YSI()1<«X1Y   F<1R    DKNTAI.   STT'DENTS. 


lation  niav  l»'.  Whether  ovulation  preeinles  or  follows  inonstrua- 
tion  is  not  known,  but  the  w.'iRht  of  evidence  favors  the  belief 
that  menstruation  serves  to  prepare  the  uterine  walls  for  tbe 
reception  of  the  fertilized  ovum  should  one  be  diseharged.  In 
animals  there  are  periods,  ealle.l  the  rutting  period,  during 
which  imprcKuation  of  the  ovum  with  the  spermatozoon  is  pos- 
sible Prece<ling  this  period  there  occurs  a  swelling  of  the  exter- 
nal genitalia  and  some  dis.-harge  of  mucus.  This  period  probably 
corresponds  to  the  menstrual  period  in  man,  for  there  is  much 
evidence  to  .show  that  impregnation  occurs  mast  freiiuently  fol- 
lowing the  men.ses. 

Menstruation  ceases  during  pregnancy  and  is  generally  absent 
•luring  the  period  of  lactation.  It  ceases  altogether  between  the 
ages  of  about  forty-five  and  fifty.  After  this  time,  which  is 
known  as  the  climacteric  i)eriod.  the  woman  is  no  longer  capable 

of  bearing  children. 

The  union  of  the  spermatozoon  and  the  ovum  usually  occurs 
in  the  oviduct.  If  the  ovum  is  not  fertilized  it  is  cast  off.  If  it 
is  fertilized,  a  considerable  thickening  of  the  uterine  mucous 
membrane  takes  place  from  the  proliferation  of  its  cells.  When 
the  ovum  reaches  the  uterus,  it  becomes  impedded  m  the  mucous 
membrane  of  the  fundus  of  the  uterus.  This  mucous  membrane 
is  very  vascular  and  soon  becomes  fused  with  the  outer  layer  of 

tlie  (,vum.  .  •  u         4. 

Pregnancy.— At  first  the  ovum  receives  its  nourishment 
directlv  from  the  mucous  membrane  of  the  uterus,  but  as  the 
ovum  develops  ami  becomes  what  we  term  an  embryo,  the  part 
lying  next  to  the  uterine  mucosa  becomes  very  vascular;  a  similar 
process  takes  i)lacc  in  the  uterine  mucosa  directly  in  contact  with 
the  embrvo.  Hv  this  process  is  formed  the  placenta,  the  organ 
through  which  the  embryo  obtains  nourishment  from  the  mother. 

The  vascular  svstem  of  the  embryo  is,  however,  entirely  sepa- 
rate from  the  maternal  vessels,  and  the  blood  of  the  mother 
never  directlv  enters  the  embryo.  The  interchange  between  the 
two  must  be  effected  through  the  cells  covering  the  vessels  of  the 
uterine  and  festal  portions  of  the  placenta.  In  other  words,  the 
embrvo  may  be  .aid  to  live  a  parasitic  yet  entirely  independent 


ni;rn<>i>i''Ti«»N. 


:!()■; 


lit".',  since  tlirouali  its  plncfiitiil  v. 
protliicts    for    tlu'    (ixy^'fii    iiiid 


iioiii-is 


cxcliiiiim's    its   fiTi'ti' 
liiiifiil    coiitaiiu'tl    in    the 


niotlii-r's  blood. 

Birth.— Wliil''    II"'   "'^■""' 


is    liciii}:  (U'Vi'lopcd  into  ii  iiuiimn 


iM'iii"  bv  division  o1'  tlu'  onjrin 


uterus  beeomes  very  inui 


ll  cetl  of  ttie  t'ertiii/e.l  ovuni.  tile 

i/e 


ll  eiilaryiiMl.  and  its  walls  ineivase  in  s 


f  niuseular  tissue.     .\t  the  end  of  api'i-ox"" 


l)y  the  fjrowtli  o 

•_'S()  ilavs  from  the  date  of  iiiipn^'iia 


mient   is  eom 


l)lete  and  birth  takes  phn 


ately 
tioll  of  the  ovum,  the  devel 
Tiiis  consists  in  the 


'xpulsion  0 
Direct 


f  the  fu'tus  by  musciilai-  ( 


ontractions  of  the  uterus. 


ly  the  child  is  born,  the  placenta  begins  to  separate  from 

11  and  is  soon  exp.-lled.     The  child  depriv.'d  of  its 

list  now  be>.'in  an  independent  life,     it 


the  uterine  \va 
placental  nourishment  in 


mus' 


t  take  in  its  own  oxy<ten  ami  Hivi 


)tV  carbon  dioxide  by  its 


respirato      orjiaii 


It  must  take  its  food  throujili  tbe  alimentary 


cana 


1.  aiiil  excivte  its  waste  pro.lucts  throujrh  its  kidneys. 


u 

X 

m 
l| 

I 


APPENDIX. 

Thorc  ar«'  hoiih-  fimdiinu'iital  truths  in  the  sji.'iic-c  of  physioloKV  whiili 

llM'  slud.iit  bf.Hl  appri-ciaH's  wIk'Ii  lu-  s.'.'S  tlir  actual  exp.Tiui.'iits  fr 

whii'h  they  art>  deduced.  Tlu-re  can  bf  no  doul.t  tliat  attual  laboratory 
work  for  ."arh  siuilmt  i«  the  Ideal  to  strive  for  in  the  teaching  of  physi- 
ology, but  limited  time  allotted  to  the  subject  and  the  expense  which 
Hudi  a  laboratory  incurs  prohibit  the  nenerai  adoption  of  the  method 
in  most  dental  schools.  The  authors  have  found  the  followliiK  experi 
ments  to  be  of  value  in  their  dental  classes,  since  tliey  increas.'  the  in- 
terest of  the  student  in  the  more  important  facts  of  the  circulatiim. 
respiration,  and  secretion.  They  are  given  as  demonstrations  Ijefore 
small  sections  of  the  class. 

Tlie  following  outlines  are  not  intended  to  give  complete  directions 
for  the  experiments,  but  to  explain  the  various  steps  of  the  experiments 
to  the  individual  students.  Full  laboratory  directions  for  all  the  experi- 
ments are  found  in  Professor  G.  N.  Stewart's  Maiiunl  of  l'lvisi;ln<ni 
(Longmans,  Ureen.  &  Co.,  I!tl4). 


DEMONSTRATION  No.  1. 

A.  The  Circulation  of  Blood  In  the  Vessels  of  the  Tadpole's  Tail. 

A  tadpole,  whose  brain  has  been  destroyed  by  a  needle  i.s  laid  on  a 
glass  slide  and  a  large  cover-glass  is  placed  over  the  tail,  which  is  then 
examined  by  the  lo'>  power  lens  of  a  microscope.  The  general  charac- 
ters of  the  flow  of  blood  through  the  vessels  can  be  seen  (p.  17!)). 

B.  The  Nature  of  the  Cardiac  Contraction. 

The  brail!  of  a  turtle  is  destroyed  by  a  sharp  blow  on  the  head.  The 
ventral  portion  of  the  carapace  is  removed  by  a  saw  cut  along  each  side 
and  bv  dissecting  it  fron.  the  tissues,  care  being  taken  to  avoid  hemor- 
rhage" The  heart,  beating  inside  the  pericardial  sac.  is  seen  posterior 
and  dorsal  to  the  pectoral  arch.  By  tying  the  fore-limbs  firmly  above 
the  head  the  pectoral  girdle  is  pulled  apart  and  more  space  is  obtained 
for  the  observation  of  the  heart.  The  pericardial  sac  is  incised  and  the 
auricles  and  ventricle  exposed.  The  auricles  appear  as  two  thin-walled 
sacs  above  and  to  each  side  of  the  ventricle  If  the  tip  of  the  ventricle 
be  raised  the  sinus  venosus  is  brought  into  vie-.  It  receiver  t.ie  supe- 
rior and  interior  vena  cava,  and  joins  the  right    -ricle. 

309 


:no 


|MlV>IOl,.MlY    yon    DKNIAI.    >'n  KK.NTS. 


At  each  canllac  cuntraCion,  .!..■  sinus  is  s.-.n  to  boa.  "-•;;.?;;';*;,• 
„„mrdla.ely  followed  by  th.  contraction  of  both  ^"■•'-'-,  ;'';',. 
in  followed  by  the  ventricular  contraction.  It  hn>n.orrhaKe  has  Inn. 
vo  eXlhc  heart  ..ur.n«  diastole  is  tilled  with  bloo.l  and  its  chan.ber« 
are  pink  and  soft,  DurinK  systole  the  chambers  become  pale.  firm,  and 
H  uaUer  In  si^e.  The  nun.ber  of  hear,  beats  per  n.lnu,.  .s  est,n,at.Mr 
•  1  R  nier-s  solution^  a  saline  solution  suitable  for  ,he  heart  poured 
Ln  the  heart,  is  seen  to  slow  the  beat,  and  warmer  solutions  increase  the 
r-,te     Heated  above  40    centlRrade  the  solution  will  stop  the  heart 

A-reco  d  o    the  auricular  and  ventricular  beat  is  unuie  by  attachi,.. 
with  a  Pin  and  string,  the  tip  of  the  auricle  »';'', ' '"';;■  ^^Ir'^'^^' 
which  write  on  the  smoked  paper  of  a  revolviuK  dn-e   I F  K,  -  )•     A 
Tra    ng  sin,ilar  to  Ki«.  LT.  is  obtained.    The  auricle  is  seen  to  beat  before 
the  ventricle.     A  .tring  tied  tightly  about   the  groove  separating  the 
auricles  and  ventricle  will  stop  the  ventricular  contraction  for  a  time, 
ZcTZ  it  removes  the  control  which  the  auricle  nornu.lly  e.xerts  on  the 
vehicle.     After  a  short   time  the  ventricle   will   begin   to   beat   aga.n. 
but  ar  a  slower  rate  and  with  no  relation  to  the  auricular  beats  (see 
p.  164). 
C.     The  Action  of  Inorganic  Salts  on  the  Heart. 

A  turtle's  heart  Is  prepared  exactly  as  in  B.    The  auricular  I  racing 
however    may  be  ousted      A  sn,al.  cannula,  tilled  -^u    Unger  s  s  U 
solution  and  attached  to  .  perfusion  bottl-  by  n.eans  "^    "';^*  ^^^^^^".^^ 
,s  inserted  through  a  V-shaped  incisi.m  e  th-r  ^'^'Vith  a  stlk  thread 
auricle  of  the  heart,  and  is  securely  tied  In  position  w  th  a  silk  thread 
The    arge  arteries  leading  fron.  the  heart  are  cut   with  a  scissors  to 
InoJ  the  Ulngers  solution  to  flow  out  freely      If.  in  place  of  K.ngers 
:luon   one  made  of  pure  sodium  chloride  and  disti'.ed  water    0.     per 
cent    is  used,  the  heart  beat  will  slow  down  and  f.naly  cease     It  a  few 
drops  of  solutions  o.  potassium  an.l  calcium  chloride  be  added        the 
TlT  the  heart  will  again  beat  normally.     If  after  restoration  ot   the 
LaJ-asoltTo    containing  only  sodium  and  potassium  salts  be  perfused 
?he  heart  will  cease  to  beat  in  extreme  .li.s.ole:  if  one  eontain.ng  oni.N 
di  m  and  calcium  is  used,  it  will  cease  to  beat  in  extreme  systole. 


A. 


ORMONSTRATION  No.  2. 
The  Factors  which  Maintain  the  Blood  Pressu.e. 


A  small  animal  i.  iai... ith  morphine,  and  ^ft-^-'/'-^^^J-; 

comes  very  d.owsv.  a  soiut.  :.  of  -eth^  ;-  -  -^  ;;  ^  "^^ -'^^ 
finn  ner  kilo  in  2n  C    C.  water,  ui).l.>    Aelg..,I    tb  ill-  '.lui  . 

the  stomalh  tube.    After  the  animal  is  co.tpletely  unconscious,  .t  is  tied 


^'m 


AITENI'lX. 


311 


„„  a  Hultabl.  op«.rat'.nr  board,  and  a  cannula  placed  In  th.  traclu-a.  Hn  » 
adUta    n.   ,ho  Hdn,i„lHtrati.,n  ..f  .-.Iut.   which   n.av   ....  nec.««ary     n 

,rde    to  "'oUHh  all  renexe«.    A  cannula  1h  inm-r...!  In  .he  caro.ld  «r  ..r> 
Tdl  a.u.    d  to  the  recording  apparatus  an  deHcrihed  on  p  no      nee 
vlt  -.1,   When  all  1h  ready,  the  drum  Ih  H.arted  at  a  «low  npe^d.  and    he 
r.;  on^he  artery  renu.ved.    A  traclnK  of  the  '''-'J.,^--:;;;::;    « 
the  individual  hear.  hea.K  U  made  on  the  drum      ^      ''      ;       ,'   ^^'^^^ 
tlon,  a  small  chanRe  in  the  preH«ure  Is  recorded,  .he  '  ■•  ^ ''^'      '    ^, 
hiihe«t    during    the    latter    par,    of    inspiration,    and    fall.n,    duriu. 
expiration. 

B.     To  Show  the  Effect  of  Varying  the  Pumpinfl  Action  of  the  Heart  on 

the  Blood  Preeeure. 

The  vaKUS  n.  rves  on  either  side  of  ,he  neck  are  found  in  ,he  sheath 

Wiethe  euro  Id  artery.    A  threa.  ,s  ,.ns  -d  loosely  about  t.oth.    A  shor 

:it'.;lrma.  tracin/is  made  o..  .     ....  dru.n,  -;;V;: j:;:;,;;" 

and  a  minute  later  the  opposite  one  is  sever^-d.    This  U  follow  ea..>  a 
markerincrease  in  the  blood  pressure  and  a  ..ulckenlng  in  the  hear 
beat     The  peripheral  end  of  the  vagus  on  one  side  Is  then  st.mu  ated 
M   means  or  electrodes  attached  to  an  induction  coll  kIvw.k  a  teta.  .z^ 
'uK^rent     The  heart  Is  slowed  or  ceases  to  beat  for  a  short  perl.u 
and  the  blood  pressure  falls  to  zero.    The  heart  soon  beats  again     or 
the  vagus  is  not  able  to  Inhibit  Its  action  for  a  long  period  of  time 
p  000)      This  experiment  shows  that  the  pumping  action  of  the  hear 
L  necessary   to  maintain   the   Mood   pressure,   and   .l>at   an    in.reased 
rate'rthe'h^art  is  accompanied  with  an  increase  in  blood  pressure, 
other  things  remaining  equal. 

C.     TO  Show  the  Effect  of  Varying  the  Peripheral  Re.i.tance  on  the 
Blood  PreMure. 

The  stimulation  of  the  splanchnic  nerve. 

Tl  e  e  t  splanchnic  nerve  Is  exposed  Just  above  the  -P-----'  -^^ 
sule  and  is  laid  on  a  pair  of  electrodes.  While  taking  a  -"-'■•-'« 
simulate  the  nerve  with  a  weak  electrical  current  and  the,  w.t^h 
8  ronger  currents.  A  great  increase  in  the  blood  pressure  ,s  obtaln,.d, 
due  to  h'  constriction  of  the  vessels  of  the  viscera  and  the  Increase 
1  the  resistance  which  they  offer  to  ,he  How  of  blood  through  ,hen, 
(see  p.  000). 

D.     To  Show  the  Actual  Change,  m  the  Kidney  Ves.ei.  Accompanying 
the  Stimulation  of  the  Splanchnic  Nerve. 
The  left  kld,H.v  i«  incased  in  a  plethysmograph.  which  is  co.inected 
with  '  ibber  tubing  to  a  tambour  equipped   .>iti.  a  wrUiuB  st;  .f .       i> 


312 


IMIYSlOl.udY    Kn|{    1>KNT.\1.    STIDKNT!^. 


1 

h  •'. 

i  >^  1, 

i 

81 


i,.crea«e  or  decrease  in  the  volume  of  the  kidney  w.U  «how  an  up  and 
down  movement  of  the  style.  The  pulse  tracing  obtained  shows  tha 
the  irstrument  records  even  small  changes  in  the  kidney  volume  It 
the  splanchnic  nerve  is  stimulated,  with  the  plethysmograph  in  place, 
there  is  a  great  decrease  in  the  .ize  of  the  kidney  as  shown  by  h 
fall  in  the  writing  style  of  the  tan.bour.  This  is  brought  about  b>  the 
great  vasoconstriction  which  accompanies  the  stimulation  ot  the  nerve 
(see  Fig.  -6). 

DEMONSTRATION  No.  3. 
Factors  which   Influence  Blood  Pressure. 
A.    The  Effect  of  Afferent  Stimuli  on  the  Respiration  and  the  Blood 
Pressure. 
The  lingual  branch  of  the  fifth  nerve  i.  exposed  on  the  under  sur- 
face of  the  jaw.  and  electrodes  are  placed  on  the  central  end  (the  end 
towards  the  brain)  of  the  divided  nerve.     While  a  normal  blood  pres- 
sure tracing  is  being  tak.'n  the  nerve  is  excited  by  stimulation  from 
an  induction  coil  with  tetanizing  shocks.    .\  rise  in  blood  pressure  and 
iueivased   respiratory   movements  are  observed   with  strong  currents 
i„  most  cases.    This  is  due  to  the  afferent  stimuli  alTectmg  the  vaso- 
n-otor  and  respiratory  centers  and  refle.xly  influencing  control  ot   the 
elTerent   respiratory  and  vascular  nerves 

B.  The   Effect  of  Stimulation  of  the  Central    End  of  the  Cut  Vagus 

Nerve. 
The  vagus  on  one  side  is  cut  and  the  central  end  is  stimulated  with 
stimuli  of  varying  strength.  With  very  weak  stimuli  a  fall  in  blood 
pressure  is  usually  produced.  Stronger  stimuli  may  produce  a  marked 
rise  in  pressure.  The  effect  is  due  to  a  reflex  stimulation  or  inhibition 
of  the  vagus  and  vasomotor  centers. 

C.  Effect  of  Haemorrhage  on  the  Blood  Pressure. 

A  cannula  is  inserted  into  the  femoral  artery,  and  while  a  normal 
blood  pressure  tracing  is  being  made,  the  artery  is  opened.  It  will  he 
found  that  when  the  artery  is  fully  opened,  there  is  an  immediate  lall 
in  blood  pressure,  due  to  lessening  of  the  peripheral  resistance.  It 
the  artery  is  onlv  partially  opened,  considerable  bleeding  may  occur 
before  the  blood  pressure  is  affected.  The  explanation  for  this  lies  in 
the  vasomotor  center  being  stimulated  by  lack  of  blood  and  causing  a 
generally  increasing  vasoconstriction  over  the  body. 
D.     The  Effect  of  Gravity  on  the  Circulation. 

Through  two  staples  on  the  under  surface  of  the  dog  board  and  op- 


AITKNDIX. 


■m:\ 


posite  tlir  insertion  of  tlie  carotid  cannii 


la  is  passed  an  iron  rod.  and  by 

■d  to  two  stout  retort  stands, 
means  ui     v  inmi/a  n.>  >..-■■  " 

A  short  piece  of  normal  blood  pressure  tracing  is  taken  on  the  drum 
and  then  at  a  Riven  moment  the  dog  is  placed  in  a  vertical  feel-down 
position,  by  rotating  the  board  (the  dog  must  be  carefully  tied  on  the 
board)  The  blood  pressure  falls,  but  shows  some  tendency  to  return 
to  normal  while  the  dog  is  still  upright.  If  the  animal  be  very  d.^eply 
under  an  an.>sthetic  there  will  be  a  very  marked  fall  in  blood  pressure 
with  no  tendency  of  the  blood  pressure  to  return,  since  the  va.somotor 
nerves  and  center  ure  no  longer  able  to  compensate  for  the  hydrostatic 
effect  of  the  blood  in  the  vertical  position  (see  p.  VX>,). 
E.     The  Effect  of  Asphyxia  on  the  Blood  Pressure  (see  p.    l:t,^,). 

\  respiratorv  tambour  is  applied  over  the  thorax  or  abdomen  and 
connected  bv  tubing  with  a  recording  tambour,  the  writing  point  of 
which  is  accuratelv  adjusted  so  as  to  write  in  the  same  vertical  line 
as  the  writing  point  of  the  mercury  manometer  The  tubing  conunL' 
iron,  the  cannula  is  clamped  and  the  effect  of  liie  resulting  asphyxia 
on  the  respiratory  movements  and  on  the  arterial  pressure  is  noted. 
The  three  stages,  as  described  on  p.  (HKI.  should  be  obtain.'d.  but  wli.  n 
the  third  stage  is  reached  the  clamp  must  be  removed  from  the  tiaclieu 
so   IS  to  allovs-  the  animal  to  recover. 

Note— 1,  the  slowing  of  th<'  heart;  2.  the  gradual,  often  insigiiilica.ii, 
ris.>  in  blood  pressure:  :!.  the  elTect  of  the  respiratory  movements  on 
the  blood  pressure.  Moth  vagus  nerv.^s  are  cut  and  the  above  experi 
ment  repeated,  noting  the  difference  in  results.  The  rise  in  blood 
pressure  is  very  gieat.  since  now  the  heart  is  no  longer  slowed  by 
the  vi-nis  stimulation  brought  by  the  excess  of  the  carbon  dioxide  in 
the  blood. 

DEMONSTRATION  No.  4. 
The  Mechanism  of  Glandular  Secretion. 
A.     Salivary   Secretion. 

The  animal  is  anesthetized  and  prepared  as  in  demonstralion   No    1 
\n  incision  is  ma.le  along  the  internal  border  of  the  .jaw  Ixme.     The 
internal  border  of  the  digastric  muscle  is  thus  exposed.     This  is  pulled 
aside  bv  a  hook  so  as  to  expose  the  transverse  tibers  of  the  mylohyoid 

muscles.     The  mvlohyoid   is  carefully   severed   following    the    li .1 

the  digastric  muscle.  The  edges  are  pulled  to  one  side  and  the  lingual 
nerve  is  s.'en  emerging  from  under  the  ramus  of  the  jaw.  In  its  trans- 
versa, course  to  the  middle  of  the  jaw.  i(  crosses  the  ducts  of  th.'  sub- 
maxillarv  and  sublingual  glands.  Where  it  crosses  the  ducts  it  giv.-s 
off  a  small  branch,  the  chorda  tympani.     A  ligature  is  placed  beneath 


pnYSKJLOOy   FOR   DENTAL   STrDENTS. 


'      !   ■ 
■I     .\   i 


!  i 


;ii4 

the  .lnB«.l  nerve  1.  divided  cen.r.l  lo   "=  "j""".  JJrt/,™„„,  „ 
cannula   is   Inserted   into  exposed  a  little  behind  the 

::r  r  j»rrier„rf ^e .  .e  d,.uo„ .  ^^^^^^^^^^^^ 

vesBels.   showing   the   presence   of   vasodilator  nerves   in 

'TfTe' cannula  in  the  duct  be  attached  to  a  mercury  -an°"eter  con- 

It  saliv^is  not  filtered  from  the  blood  into  the  salivary  tubules. 
B     Action  of  Secretin  on  Pancreatic  Secretion  (see  p.  72). 

rn7rer;rrinir":n:,:/:o*rnea.e,  .^d .... .. ... 

^r~ittnr:r''nirrjr.^i':n-:"^^^ 

^kr%SLr,.!rrd:;=;"rc.r9^^^ 

no^nt  where  the  head  of  the  pancrea.  ieaves  the  duodenum.  A  iga- 
tue  is  plced  under  it  and  the  duodenum  is  opened  by  an  incision 
along  ts  free  border.  The  cannula  is  then  inserted  through  the  open- 
Cof  he  duct  in  the  duodenum,  this  opening  being  marked  oy  a 
papilla.     It  is  then  tied  in  place  by  means  of  the  previously  applied 

"Thrdrops  of  the  secretion,  if  any,  are  counted.  20  c.  c.  of  the  secretin 
isTnjecteT  nto  .he  femoral  vein.  The  effect  is  to  produce  an  increase 
n  the  secretion.  Also  the  effect  of  the  injection  on  the  respirations 
and  the  Jl  pressure  and  pulse  should  be  noted.  The  Injections, 
using  larger  amounts  if  necessary,  are  repeated. 


n 


INDEX. 


Abducens  or  sixth  nerve.   261 
Aberration,   cliromatlc,   285 

spherical.  285 
Abborption,   80 

Accelerator  nerves  of  heart,  181 
Accommodation.    281 
mechanism,  283 
pupil    in,    284 
Acidity,  :!0 
of  gastric  juice,  64 
of  saliva,  48 
Acromegaly,    131 
Addison's    disease    and    adrenals. 

129 
Aorenalin.    130 
Adrenals    (suprarenal    capsules). 

12!t 
.Xdsorption.  33 
.M'terent  nerve  paths,  245 
Albumin,    22 
Albuminuria.  232 
Amino  bodies.  22 
.\nioeba.   18 
Animonla,   108 

in   urine.   230 
Amlopsln,  74 
Apesthesla.   245 
Analgesia.  245 
.Anaphylaxis.   151 
Animal   heat.   134 
.Antibodies  In  blood.  148 
Antlenzymes,   36.   77 
.Antipyretics,  138 
Antithrombin,  148 
Antitoxin.  130 
Apex   beat   of  heart.   162 
Aphasia.    273 
Appetite.    43,   60 
.Arterial  blood  pressure,  173 
.Asphyxia  195 

Assimilation  (s.f  Metabolism) 
As-,sociation   areas   of   cerebrum, 
272 
fibers  of  cerebrum,  272 
.Associative   memory,  273 
Asthma.   222 
Astigmatism,    286 
.Atmosphere  and   metabolism,  88 
Auditory  areas  of  cerebrum,  272 
.Auditory  ossicles,  293 
Angmentor  nerves  of  heart,  184 
Auricle.   167 
Aurlculo-ventrlcular    valves.    1!J9 


Auscultation  of  lungs.  213 
Autonomic   nervous   system.   277 

Bacterial  digestion,  66.  76 
Beat  of  heart.  161 
Beef   'ea,   107 
Beriberi,  121 
Bile,  71 

Binocular   vision.   28',< 
Bladder,  urinary,   23,''< 
Bind  spot.   288 
Blood.    140 

coagulation  of.  147 
functions  of.  140 
gases  of.   201 

microscopic  characters  of.  140 
physical  properties  of,  140 
plates.  145 
plasma.  145 
Blood   corpuscles.   140 
enumeration   of,    141 
s.Airce  of.   143 
Blood  flow,  rate  of,  179 
Blood   pressure,    173 
Uicod  vessels,  nervous  control  ot 

189 
Bodv  fat.  source  of.  115 
Bvain.  256 
Bread.    105 

Breathing,  mechanism  of.  209 
Bright's  disease.  232 
Bundle  of  His,  165 
Butter,    106 

Calcium,  120 

Calcium  salts  and  coagulation  ot 

blood,  148 
Calorimeter.    85 
Calory.  84 

Capacity  of  lungs.  216 
Carbohydrates,  24 
food   values  of.   84 
metabolism   of,    in6 
relative    metabolic    importaii'e. 
113 
Carbon    dioxide; 

effect    of    oxyhcemoglobin.    2ii2- 

206 
mechanism  of  exchange.  205 
production   of.   197 
Cardiac  cycle,  events  of,  167 
Cardiac  muscle.  163 
Cardiac    depressor   nerve.    187 
Centers,   vascular-nervous,  187 

315 


\i\i\ 


INDKX. 


in    modifying    re- 


•>Vi 


71 


nitrous 
. iratory 


('(•lebelluni.    274 
rt'reals,    105 
t'erebruni.  268 
function    of. 
flexes.  270 
localization  in.  26;t 
relation  to  recept_or  system, 
siensory   areas.   272 
Cheese.  106 

Chemical  composition  ot  body.i.i 
Chemistry,   of   bile,   7:J 
of  foods,  104 
of  gastric  juice,  64 
of  pancreatic  juice, 
of  saliva,  46 
of    urine,    22fl 
Childbirth,    307 
Cholesterol,   24 
Chor'lae  tendinese.  163 
Chyme,  68 
Ciliary  muscle,  283 
Circulation.    180 
diagram  of.  159 

influence  of  arteries,  i'-:  ''' 
cocain.  196;  of  gravity.  I'.tl; 
of  haemorrhage.  I!t4;  of  ner- 
vous svstem.  184;  of 
oxide,  1!»5;  ot  rei. 
movements.  183 
pulmonary,   182 

renal.   233 
time   of.   17i> 
venous,  178 
circulatorv  system,  anatomy 
Circumvallate   papilla?.   2'.t5 
Clothing,   136  ,_ 

Climate,  effect  of  temperature.  l..( 
Coagulation  of  blood.   147.  148 
Cocain.  196 
Colloids.  32 
Coinplemental   air.   216 
Condiments.   107 
Cones   of   retina.   287 
Consciousness.    268 
Consonants.   227 
Contraction  of  muscle.  300 

tetanic  contraction.  301 
Coordination,    function   of   cerc- 

belhnn.   274 
Cord,  spinal.  245 
Cords,   vocal.   ';25 
Cornea.   282 

Corpora  quadrigemina.   2;i( 
Corpuscles  of  blood.  141 
Corti.  organ  of.  291 
(  oughing.   214 
Cranial  nerves.  2.59 
Creatinin.   230 


15it 


174 


Cretinism.  126 
Cream,  lob 
Crying.  214 
Crystalloids,  27 
Cystine,  112 

Deglutition.  55 

Dentrite.  241 

Determination  of  blood   pressure, 

174 
Diabetes,  117 

Dialysis.   27  ,ui„  , 

Diaphragm,  relation  to  breathuu. 

210 
Diastole    of    heart,    167 
Diastolic  blood  pressure. 
Dietetics,   99 
Diet,   suitability  of.   Wl 
fundamentals   of,   lo3 

Digestion: 

hacterialiutestine, 

of  cellulose,   76 

necessity  of,  37^ 

in  intestine.  71-75 

in   mouth.   39^ 

in  stomach.  60 

object  of,  37 

resume    of    digestive    terments, 

82 
Direct  pyramidal  tract,  248 
Disaccharides,  24 
Ductless  glands.   124 
Dyspnea.   221 


76 


Kfferent  nerve  paths.  250 
b-'ggs.  106 

Klectrolyles.   28  _ 

Knamel.  action  of  saliva  on.  .;>l 
Energy   balance    (,s.<  Metabolism) 
Enterokinase,  74 
Enzymes.  34 
Erepsin,   75 
Erythrocytes.   141 
Eustachian    tube,   .'M 
,  E.xcreta,  endogenous  and  exogen- 
ous.   112 
Excretion,  from  lui.gs.  2iiti 

renal     229 
Exercist.   muscular,  and   metabol- 
ism.  114 
Exogenous  excreta.  112 
Expiration,  209 

Expired  air.  composition  ot,  -IS 
Eye  (.S(i'  Vision) 

Fat.   chemical   con.position  of.   2'! 
food  value  of,  84 
of  body,  source  of.  115 
structure  of.  24 


ll  11 


INDKX. 


317 


rflative     nii'labolic    import ance 
of.  11 H 

metabolism  of.  11" 
Ferments.  34 
Fertilization.  303 
Fetus,  nutrition  of.  306 
Fever.  137 

Fibrin,  source  of.  1-17 
Fibrinogen.    147 
Flavor.  307 
Foods,    common    composition    ol. 

104 
Fovea  centralis.  288 

Gall  bladder,  71 

stones.  74 
Ganglia.  241 
spinal.  242.  277 
sympathetic.  242.  277 
Ganglion,  definition  o..  241 
Gasserian.   261 

semilunar,  191,  278 
Gas.  absorption  of.  by  liquid.  VM\ 

partial  pressure  of.  IW 
Gases  of  blood.  201 
Gas  exchanges,  in  lungs.  217 

in  tissues,  It'S 
Gasserian   ganglion.   261 
Gastric  digestion,  Gi 
Gastric  juice,  constituents  of.  "^ 
Gastric  secretion,  control  of.  tU 
Giantism.  131 
Glands,  ductless.  124 
gastric.  60 
mammary,  238 
pancreatic,  71 
salivary.  39 
sebaceous.  238 
of  skin.  336 
sweat.  236 
thyroid.  125 
Globulin.   23 
Glomerulus.  232 
Glottis,  225 
Gluten,    104 
Glycogen.  116 
Glycoprotein.  23 
Glycosuria.   116 
Goiter.   128 
Graafian   follicle,  304 
Growth,  curve  of.  07 

Hair-cells  of  cochlea.  242 
Hoptophore  group.  150 
Hearing,  292 
Heart,  anatomy  of.   160 

BUgmentor  nerves  of.  184 

heart  block,  165 


cavities  of.  16tl 
change  in  form  of,  161 
contractions,  nviximal.  163 
influence  of  salts  on.  166 
Inhibitory  center  of.  187 
inhibitory  nerves  of.  18". 
nerves  of.    184 
passage  of  beat  o\er.  164 
pace-maker  of.  164 
physiological     peculiarities     ot, 

163 
position  of,  160 
refractory   period   of.   160 
rhythmic  action  of.  163 
sounds  of.   169 
valves  of.  162 

vascular  mechanism  of.  166 
work   of.   172 
Heart  valves.  16J 
Heat,  animal,   souices  of.   134 

value  of  foodstuffs,  85 
Hematin.   141 
Hemorrhage.  194 
Hemoglobin.   141 

absorption  of  oxygen  by.  201 
chemical  nature  of,  141 
estimation    of.   141 
influence  of  acid.  2ii2 
of  carbon  dioxide,  202 
Hiccough,  214 
Hippuric    acid,    112 
Hormones,   38.   124 
Hunger,  81 
Hydrogen  i(      .   30 

measurement   of.    31 
Hydrogen  electrode,  31 
Hydrochloric  acid  in  gastric  juice, 

64 
Hyperglyciemia,   116 
Hypothyroidism.    128 
Hyperthyroidism.   128 

Immunity,  Ehrlich's  theory  of.  l.'>o 

specific  nature  of,  151 
Immunization,   151 
Impregnation.  3it5 
Infection-resisting  mechanism.  15o 
Infiammation.  149 
Inhibitory  nerves  of  heart.  185 
Inorganic  salts,  metabolism.   119 
Inspiration.    209 
Internal  capsule,  248 
Internal   secretion,   125 
Intestinal  digestion,  75 
Intestinal  juice,  75 
Intestine,  large,  movements  of.  79 
Intestine,  small,  movements  of.  78 
Ions,  28 


318 


INDEX. 


|5!^    ■ 

\}  i   - 


Ionization,   28 
Iron,  120 

KataboUc  processes,  84 

Kephalln.   148 

Kidney,  blood  flow  through,  2S.^ 

blood  supply  of.  233 

minute  structure  of,  z.ii 

nerve  of,  333 
Knee  jerk,  251 

Lactation.  238 

lACteals,  155 

Lecithin,  24 

Lena,  crystalline.  283 

Leucocytes,  movements  of.  144 

funetlcri  of,  145 
Lipase,  in  gastric  juice.  67 

in  pancreatic  juice,  74 
Lipoids.  23 
Liver,  excretory  function  ot.  7m 

glycogenetic  function  of,  117 
Localizing  power  of  retina.  289 
Locomotor  ataxia,  254 
Lungs,  changes  of  blood  in.  21 1 

movements  of,  213 
Lymph,  movements  of,  157 

formation  of,  156 

glands,  158 

relation  of,  to  blood,  15a 

resorption  of.  157 

vessels,   157 
Lymphagogues,  156 
Lymphocytes,   144 
Lymph  nodes,  158 

Maintenance  food.  99 
Malpighian  capsule.  232 
Malpighlan    pyramids    of    kidney, 

232 
Mammary  gland,   238 
Mastication,  53 

saliva   and,   54 
Material  balance  of  body^  91 
Measurement  of  arterial  pressure, 

175 
Meat,  106 

extract,   107 
Menstruation,  304 
Mental  process,  273 
Metabolism,  general,  83 

Influence  of  atmosphere,  87 

muscular  work.  87 

surface  area,  87 

basal  neat  production,  87 

specific  dynamic  action,  87 
Metabolism,  special,  108 

carbohydrates,  116 


fats,  iir> 

Inorganic  salts,  119 

proteins.  108 
Middle  ear,  292 
Milk,  composition  of,  in.) 
Micturition.  236. 
Monosaccharides.   24 
Motor  area  of  cortex,  269 
Mountain  sickness,  222^ 
Mouth,  .ligestion  in.  4. 
Muscles.   300 
Muscle  sense,  275 
Muscular  elasticity,  301 
Muscular  energy,  source  of.  l.t.t 
Muscular  tone.  253 
Muscular    work,    expenditure    or 

energy,  99 
Myopia.  286 
Myxoedema,   127 

Nausea,  58 
Nerve: 

abducens,  261 

auditory,   264 

cranial.  259 

depressor.  187 

facial.  263 

glossopharyngeal,   264 

hypoglossal,   266 

inferior  maxillary,  2»>1 

oculomotor,  260 

olfactory,  298 

phrenic,  219 

sciatic,    219 

spinal  accessory,  265 

trlgenlnal,  261 

vagus,  265 
Nerve  Impulse,  239 
Nerve  paths,  afferent.  246 

efferent,  250 

method  of  tracing,  245 
Nerve  plexus,  240 
Nerve  system,  239 
sympathetic,  277 
Neurones,  intermediary,  247 
Nitrogen  equilibrium,   94 

balance  sheet,  94 
Nucleoprotein,  22 
Nutrition   (sri-  Metabolism) 
Nutrition  of  embryo,  306 
Nutritive  value  of  foods,  v^i 

Obesity,  treatment  of,  95 
Oculomotor  nerve,   260 
Opsonins,  163 
Optical  defects.  285 
Optic  thalami.  247 
Organ  of  Corti,  291 
Osmosis,  28 


INDF.X. 


:n9 


Osmotic  pressure.  28 

Oviduct,    304 

Ovulation.  305 

Ovum.  304 

Oxidase.    1»S 

Oxidation.  In  tissues.  198 

as  source  of  animal  heat.  IM 
Oxygen,  absorption  of,  by  blood. 

201 
Oxy  haemoglobin,     effect     of     CO 

on,  205 

Pain,  245 
Pancreatic  juL   .  71 

composition  of.   74 
Pancreatic  secretin.  72 
Pancreatic   secretion,    control    of. 

71 
Paralysis.   255 
Parathyroids,  125 
Pepsin.  64 
Pepsinogen.  64 
Peptone,  21 
Peristalsis,  79 
Perspiration.  237 
Phagocytosis.  152 
Physico-chemical  laws.  26 
Physiological  division  of  labor.  18 
Physiological   properties.    18 
Physiological  systems.  19 
Pituitary  body.  131 
Platelets,  or  plaques,  of  blood,  H.'i 
Plasma,  blood.  145 
Pneumogastric  nerves.  26.') 
Polypeptide.   22 
Pons  Varolii.  246 
Postsphygmlc  period,  167 
Potassium    sulphocyanide    in    sa- 
liva,  47 
Precipitins.  151 
Pregnancy.  306 
Presbyopia.  286 
Pressure,  arterial.   175 
Intrathoracic,  211 
osmotic.  28 
Fresphygmic  period,   167 
Properties  of  body,  physical  and 

physiological,  20 
Proteins,     chemical     composition 
of,  21 
compound,  22 
Insoluble,   23 
irreducible   minimum,   96 
nutritive  value  of,  94 
relative    metabolic    importance 

of,  113 
requirement  of  body  for,  100 
simple,  22 


sparers  of,  95 

subdivisions    of 
Proteose,  21 
Protoplasm,  composition  of.  19 

primary  constituents  of.  19 

secondary    constituents   of.   20 
Ptyalin.  47 
Puberty.    304 

Pulmonary  circulation,  182 
Pulse,  use  of.  in  diagnosis.  18" 

tracings,  180 

wave.   121 
Purin  bodies.  110 
Pyloric   sphincter,    control   of.   68 
Pylorus.  67 
Pyramidal  tracts.  248 

Range  of  voice.  226 
Rate  of  olood  flow.  179 
Reaction   of   blood.   32 

of  body  fluids.  30 
Reason,  faculty  of,  273 
Reciprocal   Inhibition,   254 
Receptors,  151,   244 
Red  blood  corpuscles,  141 
Reflex  animal,  characteristics  of. 

compared  with  normal.  251 
Reflex  arcs.  240 
Reflex    action.    252 
Reflex  paths,  244 
Reflex  time,  250 

Reflexes,  function  of  spinal  cord 
in,  2i'.0 
types  of,  25(t 
Renal   secretion.   232 
Reproduction,    sexual.   303 
Reproduetory   organs,   accessory : 

female.  304 

male.  305 
Residual   air,   216 
Respiration.   197 

artificial.    214 

control  of.   221 

external.  207 

Influence  of.  on  circulation.  213 

internal.  197 

nerves  of.  219 

volume  of  air  in.  225 
Respiratory   center.   219 

exchange,  204 

movements,  211 

organs,  207 

quotient.  91.  216 

reflex.    219 

sounds.   213 
Rickets,   120 
Rolando,  fissure  of.  269 
Roots  of  spinal  nerves,  246 


:V2() 


INDKX. 


71 


Saltva,  character  or.  46 
dental  caries  and.  r>l 
function  of.  44 
neutralizing  power  of.  4.t 
reaction   of.   48 
tartar  formation  and,  ;>! 
Salivary   calculi.   VI 
Salivary   fslands,   ;?!• 
nerve  supply  of.  40 
nervous  control  of.  \'i- 
secretion    of     :!!• 
Scratch  reflex.  2.">1 
Salt  hunger.  120  _ 
Sea   sickness,   2?" 
Sebaceous    glands.    2.'>8 
Secretin,  gastric.  6;! 

pancreatic.   71 
Secretion: 
control  of,  38 
gastric,  control  ol.  ''1 
milk.    2;i8 

pancreatic,   control   ot, 
salivary,  control  of.  41 
sebaceous.    2.38 
Secretory  process: 

hormone  control  of.  38 
nervous  control  of.  38  __ 

Semicircular   canals,    bony.    -••• 
Semilunar  ganglion,  li'l 
Semilunar  \alves.  l»>t>.  lt>.     _ 
Semipermeable  membrane...  i 
Sensory  areas  of  cortex.  -M 
Shivering.    138 
Shock.  I!t3 
Sight.    279 

Skin,  function  of.  236 
Smell.  2!>7 
Sneezing.  214 
Solutions,  isotonic.  30 
hvpertonic,  30 
hypotonic.  30 
Sound,  loudness  of.  li.^ 
Sounds  of  heart.  169 
Special  senses.  279 
Specific  dynamic  action  of  foods. 
87 

Tartar.  .52 
Taste.  296 
Taste-buds,   296 
Tectorial  membrane,  29- 
Teeth  and  fifth  nerve.  261 
Temperature  of  body.  134 
lemperature.    effect   of,    on    mus 

cular  contraction.  13!> 
Temperature  sensation  zero,  1.4.-> 
Temperature  sense,  245 


of. 


Temperature 

of.  135 
Tetany.    128 
Thorax,   contents 
movements    of.    i 

211 
Thrombin,  148 
Thrombogen,   148 
Thymus,   133 
Thyroid  gland,  12i. 
Tidal   air.   215 
Touch,  sensations 
Toxins,   bacterial. 
Toxophores    150 
Trigeminal  nerve. 
Trypsin.  74 
Trypsinogen,    74 


bodily,    regulation 


207 
respiration. 


of,  244 
149 

261 


190 


Urea.  108.  230 
Uric  acid.  110.  230 
Urinary  organs.  23- 
Urinary  salts,  nitrogen.  108 
I'rine,  ammonia,  108 

excretion    of.    229 

nature  of  excretory  process,  2.... 

Vasus  nerve,  action  of.  on  heart. 

Valves' of  heart.  162,  170 
Varicose  veins.  179 
Vasoconstrictor  nerves. 
Vasodilator  center,  18 1 
Vasodilator  nerves.  191 
Vasomotor  tone,  194 
Veins,  blood  in.  178     _ 
Velocity   of   blood.   1 1  i 
\entilation.   223 
Vision.  279 
color.   290 
stereoscopic.  290 
Visual  defects.  284_ 
treatment  of.   285 

Vital  capacity.  216 

Vitamines.    121 

Vocal  cords,  false.  224 
relation  of.  to  pitch.  2... 

Voice.  224 

Vomiting.  58 

Vowels.    227 

Water,  proportion  of.  in  body, 
phvsiolngical   properties  ol. 
Wheat    fl<.'ir,    104 
White   blood-corpuscles,    144 


20 

20 


Xanthin  bodies,   lio 
Yawning,  214 


2tt 

20 


em 


